0000950170-24-022644 | 10-K | XBRL Viewer

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Income taxes - Textual (Details) - USD ($)	12 Months Ended
Income taxes - Textual (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Income tax benefit related to operating losses and research and development tax credits	$ 0	$ 0	$ 0
Net operating loss carry forwards	88,219,000	68,450,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	12,846,000	7,704,000
Increase (Decrease) in Valuation Allowance	68,371,000	41,837,000	30,626,000
Gross unrecognized tax benefit	3,394,000	2,110,000	$ 1,313,000	$ 644,000
Accrued interest or penalties related to uncertain tax positions	0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	284,344,000
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	281,900,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	14,379,000
NOL carryforwards that expire	2,118,000
Research and development tax credit derecognized	87,000
Federal \| Research and development expense
Operating Loss Carryforwards [Line Items]
Capitalization of expenditure net of amortization, amount	$ 65,437,000	$ 57,658,000
Foreign \| Research and development expense
Operating Loss Carryforwards [Line Items]
Research and development expenditures amortization period	15 years	15 years
Capitalization of expenditure net of amortization, amount	$ 65,899,000	$ 14,728,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	413,182,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	2,355,000
NOL carryforwards that expire	3,632,000
Research and development tax credit derecognized	$ 43,000

Summary of significant accounting policies	12 Months Ended
Dec. 31, 2023
Accounting Policies [Abstract]
Summary of significant accounting policies	2. Summary of significant accounting policies Operating segment information Operating segments are defined as components of an enterprise for which separate and discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company has one operating segment. The Company’s focus is the research and development of treatments for patients with serious metabolic diseases marked by high unmet medical need, including MASH, a disease without any approved therapies. The Company’s chief operating decision maker, its chief executive officer, manages the Company’s operations on a consolidated basis for the purpose of allocating resources. Use of estimates The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the recognition of research and development expenses, stock-based compensation expense, warrant liabilities and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Cash and cash equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts. Short and long-term marketable securities The Company invests in short and long-term marketable securities, primarily money market funds, commercial paper, U.S. treasury securities and corporate debt securities. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with high ratings from top rating agencies. The Company classifies its short and long-term marketable securities as available-for-sale securities and reports them at fair value in short and long-term marketable securities on the consolidated balance sheets with related unrealized gains and losses included within accumulated other comprehensive gain (loss) on the consolidated balance sheets. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income on the consolidated statements of operations and comprehensive loss. When the fair value is below the amortized cost of a marketable security, the Company reviews and determines whether the impairment is due to credit-related factors or noncredit-related factors. The credit-related impairment amount is recognized in other income on the consolidated statements of operations and comprehensive loss, with a corresponding allowance for credit losses account in the consolidated balance sheet. Subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations. There were no credit losses recorded during the years ended December 31, 2023, 2022 and 2021. Restricted cash As of December 31, 2022, the Company was required to maintain a separate cash balance of $108 for the benefit of the landlord in connection with the Company’s Gateway office space lease in South San Francisco, California (the “Gateway Lease”), which is classified within other assets (non-current) on the consolidated balance sheets (see Note 12). The Company was not required to maintain a separate cash balance for the benefit of the landlord as of December 31, 2023. Concentrations of credit risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, short and long-term marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash investments in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. At December 31, 2023, all of the Company's cash, cash equivalents, short and long-term investments were held at four accredited financial institutions. As of December 31, 2022, the Company held cash deposits at Silicon Valley Bank ("SVB") in excess of government insured limits. On March 10, 2023, SVB was closed by the California Department of Financial Protection and Innovation, and the Federal Deposit Insurance Corporation (“FDIC”) was appointed as receiver. No losses were incurred by the Company on deposits that were held at SVB. Management believes that the Company is not currently exposed to significant credit risk as the vast majority of the Company’s deposits were either owned directly by the Company and held in custody at a third-party financial institution or, subsequent to March 10, 2023, have been transferred to a third-party financial institution. On March 27, 2023, SVB was acquired by First-Citizen BancShares, Inc ("First-Citizen"). As of December 31, 2023, the Company did not have any significant deposits on account at or relationships with SVB or First-Citizen. Leases The Company determines whether an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether the Company has the right to control the identified asset. Right-of-use, or ROU, assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and are further adjusted by any lease payments made prior to or on lease commencement, lease incentives received and initial direct costs incurred, as applicable. The Company has elected to not recognize leases with a lease term of one year or less on its balance sheet. Operating lease costs included in the measurement of the lease are recognized on a straight-line basis over the lease term. Variable lease costs are expensed as incurred as an operating expense. The Company determines the lease classification and the present value of future lease payments at the time of the lease commencement using an incremental borrowing rate that it estimates based upon the Company’s credit risk and term of the lease. The interest rate implicit in lease contracts has not historically been readily determinable and the Company must therefore use the appropriate incremental borrowing rate to measure its leases. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. Research and development costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, third-party license fees and external costs including fees paid to consultants, contract manufacturing organizations, or CMOs, and clinical research organizations, or CROs, in connection with drug product manufacturing, nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered. Foreign currency transaction gains and losses related to the purchase of contract manufacturing services are included as a component of research and development expense. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. Accrued and prepaid research and development expenses The Company has entered into various research and development and other agreements with commercial firms, researchers and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses are incurred. The Company makes estimates of accrued and prepaid research and development expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known at that time. When evaluating the adequacy of the accrued liabilities and the appropriateness of the prepaid expenses, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ materially from the Company's estimates. Stock-based compensation The Company makes stock-based awards from its stock compensation plans (see Note 8). The Company measures all stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company recognizes stock-based compensation expense for awards that contain performance-based conditions using the accelerated attribution method when management determines it is probable that the performance condition will be satisfied. The Company accounts for forfeitures as they occur. Stock-based compensation for restricted stock units is measured based on the market closing price of our common stock on the grant date. Stock-based compensation expense is recognized on a straight-line basis over the requisite service period, generally four years. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the option, the risk-free interest rate for a period that approximates the expected term of the option, and the Company's expected dividend yield. The Company currently estimates its share price volatility using a combination weighting of the historical volatility of publicly traded peer companies and the volatility of its traded share price and expects to continue to do so until mid-2025. The expected term of the Company's stock options has been determined utilizing the "simplified" method for awards that qualify as "plain-vanilla" options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. The fair value of each common stock award is estimated on the date of grant based on the fair value of the Company's common stock on that same date. Compensation expense for purchases under the Employee Stock Purchase Plan is recognized based on the fair value of the common stock estimated based on the closing price of our common stock as reported on the date of offering, less the purchase discount percentage provided for in the plan. The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified. Loan Payable Loan Payable represents the Loan and Security Agreement, dated June 15, 2022 (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), which the Company has accounted for as a debt financing arrangement. Interest expense is accrued using the effective interest rate method over the estimated period the loan will be repaid. Loan issuance costs have been recorded as a debt discount in the consolidated balance sheets and are being amortized and recorded as interest expense throughout the life of the Loan Agreement using the effective interest rate method. The Company considered whether there were any embedded features in the Loan Agreement that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification ("ASC") Topic 815, Derivatives and Hedging. Warrant Liabilities The Company accounts for warrants anticipated to be issued in the future under the Loan Agreement as liabilities and measures them at fair value using the Black-Scholes valuation model. The warrants are subject to remeasurement at each prospective balance sheet date, with any changes in the fair value recorded in the consolidated statements of operations. Income taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company's tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Net loss per share Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the Company’s net loss. Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains and losses on its short and long-term marketable securities. Recently adopted accounting pronouncements As of December 31, 2023, and for the year then ended, there were no recently adopted accounting standards that had a material impact on the Company’s consolidated financial statements. There were no recently issued accounting standards not yet adopted which would have a material effect on the Company’s consolidated financial statements. Recently Issued Accounting Standards Not Yet Adopted In December 2023, the Financial Accounting Standards Board (“FASB”), issued Accounting Standards Update (“ASU”) No. 2023-09, Income Taxes (Topic 740), Improvements to Income Tax Disclosures, to enhance the transparency and decision usefulness of income tax disclosures. The enhancement will provide information to better assess how an entity’s operations and related tax risks and tax planning and operational opportunities affect its tax rate and prospects for future cash flows. Investors currently rely on the rate reconciliation table and other disclosures, including total income taxes paid, to evaluate income tax risks and opportunities. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-09 will have on its consolidated financial statements and related disclosures. In November 2023, the FASB, issued ASU No. 2023-07, Segment Reporting (Topic 280), Improvements to Reportable Segment Disclosures, to improve reportable segment disclosure requirements. The amendment introduced new requirements to disclose significant segment expenses regularly provided to the chief operating decision maker (“CODM”) and extend certain annual disclosures to interim periods. Entities with a single reportable segment must apply ASC 280 in its entirety, are permitted to report more than one measure of segment profit or or loss under certain conditions and are required to disclose the title and position of the CODM. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-07 will have on its consolidated financial statements and related disclosures.

Summary of significant accounting policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of significant accounting policies

2. Summary of significant accounting policies

Operating segment information

Operating segments are defined as components of an enterprise for which separate and discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company has one operating segment. The Company’s focus is the research and development of treatments for patients with serious metabolic diseases marked by high unmet medical need, including MASH, a disease without any approved therapies. The Company’s chief operating decision maker, its chief executive officer, manages the Company’s operations on a consolidated basis for the purpose of allocating resources.

Use of estimates

The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the recognition of research and development expenses, stock-based compensation expense, warrant liabilities and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Cash and cash equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts.

Short and long-term marketable securities

The Company invests in short and long-term marketable securities, primarily money market funds, commercial paper, U.S. treasury securities and corporate debt securities. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with high ratings from top rating agencies. The Company classifies its short and long-term marketable securities as available-for-sale securities and reports them at fair value in short and long-term marketable securities on the consolidated balance sheets with related unrealized gains and losses included within accumulated other comprehensive gain (loss) on the consolidated balance sheets. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income on the consolidated statements of operations and comprehensive loss. When the fair value is below the amortized cost of a marketable security, the Company reviews and determines whether the impairment is due to credit-related factors or noncredit-related factors. The credit-related impairment amount is recognized in other income on the consolidated statements of operations and comprehensive loss, with a corresponding allowance for credit losses account in the consolidated balance sheet. Subsequent improvements in expected credit losses are recognized as a reversal of an

amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations. There were no credit losses recorded during the years ended December 31, 2023, 2022 and 2021.

Restricted cash

As of December 31, 2022, the Company was required to maintain a separate cash balance of $108 for the benefit of the landlord in connection with the Company’s Gateway office space lease in South San Francisco, California (the “Gateway Lease”), which is classified within other assets (non-current) on the consolidated balance sheets (see Note 12). The Company was not required to maintain a separate cash balance for the benefit of the landlord as of December 31, 2023.

Concentrations of credit risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, short and long-term marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash investments in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. At December 31, 2023, all of the Company's cash, cash equivalents, short and long-term investments were held at four accredited financial institutions.

As of December 31, 2022, the Company held cash deposits at Silicon Valley Bank ("SVB") in excess of government insured limits. On March 10, 2023, SVB was closed by the California Department of Financial Protection and Innovation, and the Federal Deposit Insurance Corporation (“FDIC”) was appointed as receiver. No losses were incurred by the Company on deposits that were held at SVB. Management believes that the Company is not currently exposed to significant credit risk as the vast majority of the Company’s deposits were either owned directly by the Company and held in custody at a third-party financial institution or, subsequent to March 10, 2023, have been transferred to a third-party financial institution. On March 27, 2023, SVB was acquired by First-Citizen BancShares, Inc ("First-Citizen"). As of December 31, 2023, the Company did not have any significant deposits on account at or relationships with SVB or First-Citizen.

Leases

The Company determines whether an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether the Company has the right to control the identified asset. Right-of-use, or ROU, assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and are further adjusted by any lease payments made prior to or on lease commencement, lease incentives received and initial direct costs incurred, as applicable. The Company has elected to not recognize leases with a lease term of one year or less on its balance sheet. Operating lease costs included in the measurement of the lease are recognized on a straight-line basis over the lease term. Variable lease costs are expensed as incurred as an operating expense.

The Company determines the lease classification and the present value of future lease payments at the time of the lease commencement using an incremental borrowing rate that it estimates based upon the Company’s credit risk and term of the lease. The interest rate implicit in lease contracts has not historically been readily determinable and the Company must therefore use the appropriate incremental borrowing rate to measure its leases. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, third-party license fees and external costs including fees paid to consultants, contract manufacturing organizations, or CMOs, and clinical research organizations, or CROs, in connection with drug product manufacturing, nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered.

Foreign currency transaction gains and losses related to the purchase of contract manufacturing services are included as a component of research and development expense.

Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses.

Accrued and prepaid research and development expenses

The Company has entered into various research and development and other agreements with commercial firms, researchers and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses are incurred. The Company makes estimates of accrued and prepaid research and development expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known at that time. When evaluating the adequacy of the accrued liabilities and the appropriateness of the prepaid expenses, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ materially from the Company's estimates.

Stock-based compensation

The Company makes stock-based awards from its stock compensation plans (see Note 8). The Company measures all stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company recognizes stock-based compensation expense for awards that contain performance-based conditions using the accelerated attribution method when management determines it is probable that the performance condition will be satisfied. The Company accounts for forfeitures as they occur. Stock-based compensation for restricted stock units is measured based on the market closing price of our common stock on the grant date. Stock-based compensation expense is recognized on a straight-line basis over the requisite service period, generally four years.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the option, the risk-free interest rate for a period that approximates the expected term of the option, and the Company's expected dividend yield. The Company currently estimates its share price volatility using a combination weighting of the historical volatility of publicly traded peer companies and the volatility of its traded share price and expects to continue to do so until mid-2025. The expected term of the Company's stock options has been determined utilizing the "simplified" method for awards that qualify as "plain-vanilla" options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future.

The fair value of each common stock award is estimated on the date of grant based on the fair value of the Company's common stock on that same date.

Compensation expense for purchases under the Employee Stock Purchase Plan is recognized based on the fair value of the common stock estimated based on the closing price of our common stock as reported on the date of offering, less the purchase discount percentage provided for in the plan.

The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified.

Loan Payable

Loan Payable represents the Loan and Security Agreement, dated June 15, 2022 (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), which the Company has accounted for as a debt financing arrangement. Interest expense is accrued using the effective interest rate method over the estimated period the loan will be repaid. Loan issuance costs have been recorded as a debt discount in the consolidated balance sheets and are being amortized and recorded as interest expense throughout the life of the Loan Agreement using the effective interest rate method. The Company considered whether there were any embedded features in the Loan Agreement that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification ("ASC") Topic 815, Derivatives and Hedging.

Warrant Liabilities

The Company accounts for warrants anticipated to be issued in the future under the Loan Agreement as liabilities and measures them at fair value using the Black-Scholes valuation model. The warrants are subject to remeasurement at each prospective balance sheet date, with any changes in the fair value recorded in the consolidated statements of operations.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company's tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Net loss per share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the Company’s net loss.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains and losses on its short and long-term marketable securities.

Recently adopted accounting pronouncements

As of December 31, 2023, and for the year then ended, there were no recently adopted accounting standards that had a material impact on the Company’s consolidated financial statements. There were no recently issued accounting standards not yet adopted which would have a material effect on the Company’s consolidated financial statements.

Recently Issued Accounting Standards Not Yet Adopted

In December 2023, the Financial Accounting Standards Board (“FASB”), issued Accounting Standards Update (“ASU”) No. 2023-09, Income Taxes (Topic 740), Improvements to Income Tax Disclosures, to enhance the transparency and decision usefulness of income tax disclosures. The enhancement will provide information to better assess how an entity’s operations and related tax risks and tax planning and operational opportunities affect its tax rate and prospects for future cash flows. Investors currently rely on the rate reconciliation table and other disclosures, including total income taxes paid, to evaluate income tax risks and opportunities. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-09 will have on its consolidated financial statements and related disclosures.

In November 2023, the FASB, issued ASU No. 2023-07, Segment Reporting (Topic 280), Improvements to Reportable Segment Disclosures, to improve reportable segment disclosure requirements. The amendment introduced new requirements to disclose significant segment expenses regularly provided to the chief operating decision maker (“CODM”) and extend certain annual disclosures to interim periods. Entities with a single reportable segment must apply ASC 280 in its entirety, are permitted to report more than one measure of segment profit or or loss under certain conditions and are required to disclose the title and position of the CODM. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-07 will have on its consolidated financial statements and related disclosures.

Stock based awards - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Number of Options
Balance Outstanding, Beginning of the period (in shares)	5,780,004
Options granted ( in shares)	1,720,882
Options exercised ( in shares)	(593,959)
Options cancelled (in shares)	(6,950)
Balance Outstanding, End of the period (in shares)	6,899,977	5,780,004
Vested and expected to vest ( in shares)	6,899,977
Exercisable ( in shares)	4,126,549
Weighted-Average Exercise Price per Share
Weighted-average exercise price, Beginning of the period (in dollars per share)	$ 18.88
Weighted-average exercise price, Granted (in dollars per share)	28.29
Weighted-average exercise price, Exercised (in dollars per share)	5.5
Weighted-Average Exercise price, cancelled (in dollars per share)	49.74
Weighted-average exercise price, End of the period (in dollars per share)	22.35	$ 18.88
Weighted-average exercise price, Vested and expected to vest at end of the period (in dollars per share)	22.35
Weighted-average exercise price, Exercisable ( in dollars per share )	$ 18.32
Weighted-Average remaining contractual term (years) and Aggregate Intrinsic Value
Weighted-average remaining contractual term outstanding (in years)	7 years 8 months 1 day	7 years 9 months 18 days
Weighted-average remaining contractual term vested and expected to vest (in years)	7 years 8 months 1 day
Weighted-average remaining contractual term , Options Exercisable(in years)	6 years 8 months 8 days
Aggregate Intrinsic Value Balance outstanding	$ 35,133	$ 207,611
Aggregate Intrinsic Value Vested and Expected to vest	35,133
Aggregate Intrinsic Value Exercisable	$ 28,508
Weighted average grant-date fair value per share of stock options granted	$ 28.29	$ 28.76	$ 13.98

Stock based awards - Stock-based compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock-based compensation
Total stock-based compensation expense	$ 21,497	$ 23,243	$ 10,054
Research and development expense
Stock-based compensation
Total stock-based compensation expense	7,579	8,096	3,054
General and administrative expense
Stock-based compensation
Total stock-based compensation expense	$ 13,918	$ 15,147	$ 7,000

Fair value of financial assets and liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of assets and liabilities measured at fair value on a recurring basis

The following is a summary of our financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022:


	December 31, 2023
	Total		Level 1		Level 2		Level 3
Money market funds	$	206,879	$	206,879	$	—	$	—
U.S. Treasury securities		117,307		117,307		—		—
U.S. Government agency securities		133,297		—		133,297		—
Commercial paper		68,708		—		68,708		—
Corporate debt securities		15,774		—		15,774		—
Total assets	$	541,965	$	324,186	$	217,779	$	—

Warrant liabilities	$	54	$	—	$	—	$	54
Total liabilities	$	54	$	—	$	—	$	54

	December 31, 2022
	Total		Level 1		Level 2		Level 3
Money market funds	$	137,286	$	137,286	$	—	$	—
U.S. Treasury securities		58,721		58,721		—		—
Corporate debt securities		5,476		—		5,476		—
U.S. Government agency securities		62,955		—		62,955		—
Commercial paper		27,738		—		27,738		—
Total assets	$	292,176	$	196,007	$	96,169	$	—

Warrant liabilities	$	305	$	—	$	—	$	305
Total liabilities	$	305	$	—	$	—	$	305

Commitments and contingencies (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jul. 10, 2020 ft²	Feb. 29, 2020 USD ($)
Lease agreement term				7 years
Square feet of office \| ft²			6,647
Minimum payments during the term				$ 2,300
Non-cancelable purchase and other commitments with contract research organizations and contract manufacturing organizations	$ 30,878
Total lease liability	1,079
Operating lease liability, noncurrent	$ 819	$ 1,079
Accounting Standards Update 2016-13 [Member]
Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Operating lease liability, noncurrent, Prepaid Expense and Other Assets, Current
Short-term Liabilities	$ 260

Income taxes - Income tax rate (Details)	12 Months Ended
Income taxes - Income tax rate (Details)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	18.50%	13.00%	7.20%
Research and development tax credits	2.40%	2.40%	2.00%
Other permanent differences	2.60%	0.80%	(0.10%)
Change in deferred tax asset valuation allowance	(44.50%)	(37.20%)	(30.10%)

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 234,207	$ 249,773
Short-term marketable securities	315,803	101,676
Prepaid expenses and other current assets	9,952	3,724
Total current assets	559,962	355,173
Long-term marketable securities	19,283
Property and equipment, net	18	47
Right of use asset	1,008	1,242
Other assets, noncurrent		108
Total assets	580,271	356,570
Current liabilities:
Accounts payable	7,038	7,968
Accrued expenses and other current liabilities	12,090	11,115
Total current liabilities	19,128	19,083
Loan payable, noncurrent	24,964	9,541
Warrant liability	54	305
Operating lease liability, noncurrent	819	1,079
Total liabilities	44,965	30,008
Commitments and contingencies (Note 12)
Stockholders' equity:
Common stock, $0.0001 par value, 150,000,000 shares authorized as of December 31, 2023 and December 31, 2022; 55,754,445 and 46,865,206 shares issued and outstanding as of December 31, 2023 and December 31, 2022, respectively	6	5
Additional paid-in capital	1,109,126	748,857
Accumulated other comprehensive income	270	37
Accumulated deficit	(574,096)	(422,337)
Total stockholders' equity	535,306	326,562
Total liabilities and stockholders' equity	$ 580,271	$ 356,570

Commitments and contingencies - Components of operating lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating lease expense:
Total operating lease cost	$ 522	$ 440	$ 341
Other information:
Cash paid for amounts included in the measurement of operating lease liability	$ 321	$ 312	$ 303
Weighted average remaining lease term (years)	3 years 7 months 6 days	4 years 7 months 6 days	5 years 7 months 6 days
Weighted average discount rate	7.60%	7.60%	7.60%
General and administrative expense
Operating lease expense:
Operating lease cost	$ 324	$ 324	$ 324
Short-term lease cost	161	58
Variable operating lease cost	$ 37	$ 58	$ 17

Loan Payable and Warrant Liability - Textual (Details)				3 Months Ended	12 Months Ended
Loan Payable and Warrant Liability - Textual (Details)	Feb. 28, 2024 USD ($) shares	Mar. 10, 2023 USD ($) shares	Jun. 15, 2022 USD ($) Tranche	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares
Debt Instrument [Line Items]
Proceeds from term loan					$ 15,000,000	$ 10,000,000
Amortization of debt issuance costs and discount					$ 448,000	$ 204,000
Common stock, par value (in dollars per share) \| $ / shares					$ 0.0001	$ 0.0001
Fair value change in warrant liability					$ 79,000	$ 264,000
Hercules
Debt Instrument [Line Items]
Issued warrants to purchase shares of common stock \| shares		9,180
Loan Agreement
Debt Instrument [Line Items]
End of term charge of outstanding principal balance, in percentage			5.85%
Amortization of debt issuance costs and discount			$ 1,463,000
Issued warrants to purchase shares of common stock \| shares					36,718
Recognized initial warrants at relative fair value					$ 227,000
Additional remaining warrants were recognized at relative fair value at closing of agreement					41,000
Fair value associated with equity and liability classified warrants					268,000
Warrant liabilities					54,000	$ 305,000
Fair value change in warrant liability					$ 79,000
Loan Agreement \| First Twelve Months After Closing
Debt Instrument [Line Items]
Percentage of prepayment charge of outstanding principal balance			3.00%
Loan Agreement \| Second Twelve Months After Closing
Debt Instrument [Line Items]
Percentage of prepayment charge of outstanding principal balance			2.00%
Loan Agreement \| Thereafter
Debt Instrument [Line Items]
Percentage of prepayment charge of outstanding principal balance			1.00%
Loan Agreement \| Hercules
Debt Instrument [Line Items]
Proceeds from term loan				$ 15,000,000
Loan Agreement \| Term Loan \| Hercules
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 100,000,000
Number of tranches available for loan \| Tranche			4
Proceeds from term loan			$ 10,000,000
Term loan, description					Under the terms of the Loan Agreement, the Company received $10,000 upon closing, $15,000 was borrowed in March of 2023 and $30,000 remains available to the Company to borrow at its sole discretion until March 15, 2024. An additional $45,000 may become available to the Company at Hercules' sole discretion.
Maturity date			Jan. 01, 2027
Variable annual rate			7.65%
Loan Agreement \| Term Loan \| Hercules \| Subsequent Event
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 150,000,000
Proceeds from term loan	$ 10,000,000
Issued warrants to purchase shares of common stock \| shares	18,359
Loan Agreement \| Term Loan \| Hercules \| Prime Rate
Debt Instrument [Line Items]
Variable annual rate			3.65%
Loan Agreement \| Term Loan First Tranche
Debt Instrument [Line Items]
Remaining borrowing capacity					$ 10,000,000
Additional loan advances available					$ 10,000,000
Loan Agreement \| Term Loan First Tranche \| Hercules
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 45,000,000
Remaining borrowing capacity			30,000,000
Proceeds from term loan		$ 15,000,000	15,000,000
Additional loan advances available			$ 30,000,000
Warrants to Purchase Common Stock \| Loan Agreement \| Term Loan \| Hercules
Debt Instrument [Line Items]
Common stock, par value (in dollars per share) \| $ / shares					$ 0.0001
Maximum percentage of warrants purchased					1.50%

Income taxes - Valuation allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Valuation allowance as of January 1,	$ (108,690)	$ (66,853)
Decreases recorded as a benefit to income tax provision	(68,371)	(41,837)
Valuation allowance as of December 31,	$ (177,061)	$ (108,690)

Fair value of financial assets and liabilities - Recurring (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 541,965	$ 292,176
Liabilities	54	305
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	206,879	137,286
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	117,307	58,721
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	15,774	5,476
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	133,297	62,955
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	68,708	27,738
Warrant liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	54	305
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	324,186	196,007
Level 1 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	206,879	137,286
Level 1 \| U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	117,307	58,721
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	217,779	96,169
Level 2 \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	15,774	5,476
Level 2 \| U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	133,297	62,955
Level 2 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	68,708	27,738
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	54	305
Level 3 \| Warrant liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities	$ 54	$ 305

Stock-based awards - Summary of Restricted Stock activity (Details) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Balance Outstanding, Beginning of the period (in shares)	129,131
Underlying shares, Granted	281,462	129,131
Underlying shares, vested	(38,641)
Balance Outstanding, End of the period (in shares)	371,952	129,131
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average grant date fair value per share beginning balance	$ 42.95
Weighted average grant date fair value per share granted	24.03	$ 42.95
Weighted average grant date fair value per share vested	43.94
Weighted average grant date fair value per share ending balance	$ 28.53	$ 42.95
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Weighted-Average remaining contractual term (years)	1 year 11 months 23 days	2 years 25 days
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value [Abstract]
Aggregate Intrinsic Value (000's)	$ 8,685	$ 7,076

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (151,759)	$ (112,033)	$ (100,777)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	21,497	23,243	10,054
Depreciation	29	43	41
Non-cash lease expense	234	217	203
Net amortization of premiums and discounts on short-term investments	(9,554)	(12)	1,066
Amortization of debt issuance costs and discount	448	204
Fair value change in warrant liability	79	264
Write-off of deferred offering costs	337
Unrealized foreign exchange gain and loss	(8)	16	5
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(6,740)	2,112	(2,101)
Accounts payable	(645)	968	3,273
Accrued expenses and other current liabilities	946	(7,333)	8,737
Operating lease liability	(231)	(206)	(182)
Net cash used in operating activities	(145,367)	(92,517)	(79,681)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of short-term and long-term marketable securities	(433,123)	(101,446)	(43,561)
Proceeds from maturities of short-term marketable securities	209,500	37,621	85,841
Net cash (used in) provided by investing activities	(223,623)	(63,825)	42,280
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the exercise of stock options	3,267	5,016	750
Proceeds from the issuance of common stock pursuant to employee stock purchase plan purchases	396	280	373
Proceeds from the issuance of common in a follow-on public offering		216,200
Proceeds from the issuance of common stock pursuant to the ATM offering	124,212
Proceeds from the issuance of common stock pursuant to registered direct offering	211,217
Proceeds from the issuance of common stock pursuant to private offering		25,000
Proceeds from loan payable	15,000	10,000
Payment of debt and equity issuance costs	(776)	(864)	(521)
Net cash provided by financing activities	353,316	255,632	602
Net (decrease) increase in cash, cash equivalents and restricted cash	(15,674)	99,290	(36,799)
Cash, cash equivalents and restricted cash at the beginning of the period	249,881	150,591	187,390
Cash, cash equivalents and restricted cash at the end of the period	234,207	249,881	150,591
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest	2,483	441
NON-CASH INVESTING AND FINANCING INFORMATION:
Change in net unrealizable gain (loss) on marketable securities	$ 233	64	$ (24)
Warrant liability costs reclassified to additional paid-in equity on vested warrants issued	330
Debt and equity issuance costs included in accounts payable and accrued expenses and other current liabilities		285
Deferred offering costs reclassified to additional paid-in equity	$ 364	$ 150

Stock-based awards - Textual (Details) - USD ($)		1 Months Ended		12 Months Ended
Stock-based awards - Textual (Details) - USD ($)	Jun. 18, 2019	Jan. 31, 2022	Jun. 30, 2019	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 31, 2023
Share-based awards
Number of shares remained available for grant				13,667,341	14,318,383
Weighted average grant-date fair value per share of stock options granted				$ 28.29	$ 28.76	$ 13.98
Stock options granted ( in shares)				1,720,882
Exercise price				$ 28.29
Stock compensation expense				$ 21,497,000	$ 23,243,000	$ 10,054,000
Total unrecognized compensation cost related to unvested stock-based awards				51,121,000
Total unrecognized compensation cost related to RSU				$ 10,331,000
Weighted average period of recognition for unrecognized compensation cost				2 years 10 months 13 days
Performance Shares
Share-based awards
Stock options granted ( in shares)						610,546
Additional stock options granted (in shares)		248,376
Exercise price		$ 21.7				$ 21.1
Stock compensation expense				$ 10,487,000
Options vesting description				One-third of the options vest upon achievement of each of the milestones.
Description of milestones achieved and deemed vested				In September 2022, two of the three performance-based awards milestones were achieved and were deemed vested
Restricted Stock Units
Share-based awards
Weighted average period of recognition for unrecognized compensation cost				3 years 7 months 9 days
RSU granted (shares)				281,462	129,131
Weighted average grant-date fair value per share of RSUs granted				$ 24.03	$ 42.95
Total grant date fair value of RSU					$ 5,546,000
Restricted Stock Units \| Executive and Non-executive Employees
Share-based awards
RSU granted (shares)				281,462
Total grant date fair value of RSU				$ 24,030.00
2018 Stock option and grant plan
Share-based awards
Number of shares of common stock issued	3,071,960
Number of shares remained available for grant	107,635			1,114,189	1,633,173
2019 Stock option and incentive plan
Share-based awards
Number of shares remained available for grant	107,635
Number of shares initially reserved for issuance			2,572,457
Number of additional shares reserved for issuance		1,396,029					1,874,608
Percent of shares reserved and available for issuance automatically increase annually on January 1			4.00%
Percentage of exercise price per share of stock options			100.00%
Percentage of minimum exercise price, holding more than 10% of voting power			110.00%
Stock options vesting period			4 years
2019 Employee stock purchase plan
Share-based awards
Number of shares initially reserved for issuance	273,869
Number of additional shares reserved for issuance		349,007					410,803
Percent of shares reserved and available for issuance automatically increase annually on January 1			1.00%
Number of shares reserved and available for issuance automatically increase annually on January 1 (in shares)			410,803
Maximum \| 2019 Stock option and incentive plan
Share-based awards
Term of stock option			10 years

Accrued expenses and other current liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Accrued expenses and other current liabilities

Schedule of accrued expenses and other current liabilities

The following is a summary of accrued expenses and other current liabilities as of December 31, 2023 and 2022:


	December 31, 2023		December 31, 2022
Accrued external research and development expenses	$	10,041	$	9,789
Accrued employee compensation and benefits		1,296		804
Accrued legal and professional fees		231		197
Short-term lease liability and other		522		325
	$	12,090	$	11,115

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (151,759)	$ (112,033)	$ (100,777)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-3

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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+ Details

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 141,798	$ 85,284	$ 81,759
General and administrative	31,072	29,872	19,127
Total operating expenses	172,870	115,156	100,886
Loss from operations	(172,870)	(115,156)	(100,886)
Interest expense	(3,099)	(739)
Interest and other income, net	24,210	3,862	109
Net loss	(151,759)	(112,033)	(100,777)
Net unrealized gain (loss) on marketable securities	233	64	(24)
Comprehensive loss	$ (151,526)	$ (111,969)	$ (100,801)
Net loss per share, basic	$ (2.89)	$ (2.87)	$ (2.89)
Net loss per share, diluted	$ (2.89)	$ (2.87)	$ (2.89)
Weighted-average number of shares used in computing net loss per common share, basic	52,568,159	38,984,772	34,827,385
Weighted-average number of shares used in computing net loss per common share, diluted	52,568,159	38,984,772	34,827,385

Stockholder's equity (deficit) (Tables)

12 Months Ended

Dec. 31, 2023

Stockholders' Equity Note [Abstract]

Schedule of common stock reserved for issuance

The following shares of common stock were reserved for issuance as follows:


	December 31, 2023		December 31, 2022
Options outstanding under the 2018 Stock Option and Grant Plan		1,114,189		1,633,173
Options outstanding under the 2019 Stock Option and Incentive Plan		5,785,788		4,146,831
Restricted stock units outstanding under the 2019 Stock Option and Incentive Plan		371,952		129,131
Warrants to purchase common stock associated with Loan Agreement		45,898		36,718
Options available for future grant		1,917,356		2,038,142
Warrants available for future grant		137,700		146,880
Common stock available for ATM program		2,708,234		5,000,000
2019 Employee Stock Purchase Plan		1,586,224		1,187,508
		13,667,341		14,318,383

Insider Trading Arrangements

3 Months Ended

Dec. 31, 2023

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

The following table describes contracts, instructions or written plans for the sale or purchase of our securities adopted by our directors and certain officers during the quarter ended December 31, 2023, each of which is intended to satisfy the affirmative defense conditions of Exchange Act Rule 10b5-1(c), referred to as Rule 10b5-1 trading plans.

      Name and Title

      Date and Action Taken

      Duration of Trading Arrangement

      Aggregate Number of Securities to be sold or purchased

      Jonathan Young, 
Chief Operating Officer

      Plan adopted on December 27, 2023

      276 days

      30,000

Rule 10b5-1 Arrangement Adopted

true

Jonathan Young

Trading Arrangements, by Individual

Name

Jonathan Young

Title

Chief Operating Officer

Adoption Date

December 27, 2023

Arrangement Duration

276 days

Aggregate Available

30,000

Subsequent event - Textual (Details) - USD ($)					3 Months Ended	12 Months Ended
Subsequent event - Textual (Details) - USD ($)	Feb. 28, 2024	Feb. 14, 2024	Mar. 10, 2023	Jun. 15, 2022	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Subsequent Event [Line Items]
Proceeds from term loan						$ 15,000,000	$ 10,000,000
Net proceeds through sale of shares						$ 818,900,000
Loan Agreement
Subsequent Event [Line Items]
Issued warrants to purchase shares of common stock						36,718
Term Loan First Tranche \| Loan Agreement
Subsequent Event [Line Items]
Remaining borrowing capacity						$ 10,000,000
Hercules
Subsequent Event [Line Items]
Issued warrants to purchase shares of common stock			9,180
Hercules \| Loan Agreement
Subsequent Event [Line Items]
Proceeds from term loan					$ 15,000,000
Hercules \| Term Loan \| Loan Agreement
Subsequent Event [Line Items]
Maximum borrowing capacity				$ 100,000,000
Proceeds from term loan				10,000,000
Hercules \| Term Loan First Tranche \| Loan Agreement
Subsequent Event [Line Items]
Maximum borrowing capacity				45,000,000
Proceeds from term loan			$ 15,000,000	15,000,000
Remaining borrowing capacity				$ 30,000,000
Subsequent Event \| ATM Facility
Subsequent Event [Line Items]
Net proceeds through sale of shares		$ 10,603,000
Shares sold		500,000
Average price per share		$ 21.75
Subsequent Event \| Hercules \| Term Loan \| Loan Agreement
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 150,000,000
Proceeds from term loan	$ 10,000,000
Issued warrants to purchase shares of common stock	18,359

Loan Payable and Warrant Liability

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Loan Payable and Warrant Liability

6. Loan Payable and Warrant Liability

On June 15, 2022, the Company entered into a Loan and Security Agreement (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), for an aggregate principal amount of $100,000 (“Term Loan”). Pursuant to the Loan Agreement, the Term Loan is available to the Company in four tranches, subject to certain terms and conditions.

Under the terms of the Loan Agreement, the Company received $10,000 upon closing, $15,000 was borrowed in March of 2023 and $30,000 remains available to the Company to borrow at its sole discretion until March 15, 2024. An additional $45,000 may become available to the Company at Hercules' sole discretion.

The Term Loan will mature on January 1, 2027 (the “Maturity Date”). The Term Loan bears interest at a variable annual rate equal to the greater of (a) 7.65% and (b) the Prime Rate (as reported in the Wall Street Journal) plus 3.65% (the “Interest Rate”). The Company may make payments of interest only through July 1, 2025 (the “interest-only period”). After the interest-only period, the principal balance and related interest will be required to be repaid in equal monthly installments and continuing until the Maturity Date.

The Loan Agreement contains customary closing fees, events of default, and representations, warranties and covenants, including a financial covenant requiring the Company to maintain a minimum cash balance in relation to the outstanding principal balance of the Term Loan. The Loan Agreement is secured by most of the Company's assets, including its bank and investment accounts. The Loan Agreement provides for a prepayment charge equal to 3% of the outstanding principal balance of the Term Loan if prepayment is made within the first twelve months after closing, 2% if within the second twelve months after closing and 1% thereafter. In addition, the Loan Agreement provides for an End of Term Charge that will be the greater of 5.85% of the outstanding principal balance or $1,463, which is recognized as a debt discount and is being accreted into the amortization of debt issuance costs and discount using the effective interest rate method over the term of the loan payable.

Upon closing, the Company issued warrants to Hercules to purchase shares of the Company’s common stock, par value $0.0001 per share ("common stock"). The amount of shares that may be purchased for the Warrants will not exceed 1.5% multiplied by the greater of Tranche I and the aggregate original amount of the term loan advances, divided by the exercise price of the Warrants.

The Company was in compliance with all covenants of the Loan Agreement as of December 31, 2023.

The Company determined in accordance with ASC 480-10 that the initial tranche one advance of $10,000, the additional Term Loan advances available under tranches one, two, three and four and the warrants issued upon closing shall be accounted for as freestanding financial instruments as they are legally detachable and separately exercisable. The Company also determined in accordance with ASC 815-10 that the additional Term Loan advances available under tranches one, two, three and four do not qualify as derivative instruments and that the value associated with these commitments is immaterial.

Upon closing, the Company issued to Hercules warrants to purchase 36,718 shares of Company’s common stock and recognized the initial warrants at their relative fair value of $227 in shareholders equity. In accordance with ASC 815-40, the additional remaining warrants to purchase shares of the Company’s common stock at the closing of the Loan Agreement were recognized at their fair value of $41 as warrant liabilities given the variable settlement amount of the warrant shares. The additional remaining warrants under the Loan Agreement are considered an outstanding instrument at close of the Loan Agreement. The total fair value of $268 associated with these equity and liability classified warrants, is recognized as a debt discount and is being accreted into the amortization of debt issuance costs and discount using the effective interest rate method over the term of the loan payable. The Company reassesses the fair value of the warrant liability at the end of each prospective reporting period.

In March 2023, the Company borrowed an additional $15,000 and issued warrants to Hercules to purchase an additional 9,180 shares of Company's common stock. The fair value associated with these additional warrants of $330 were reclassified from warrant liability to additional paid in capital.

The warrant liabilities were valued at $54 and $305 as of December 31, 2023 and 2022, respectively. The change in fair value of the warrant liability of $79 from December 31, 2022 to December 31, 2023 arising from remeasurement was recorded in the statements of operations.

Future principal debt payments on the currently outstanding loan payable as of December 31, 2023 and 2022 are as follows (in thousands):


		Year Ended December 31,
			2023			2022
2023	$		—		$	—
2024			—			1,710
2025			7,343			3,725
2026			16,118			4,169
2027			1,539			396
Total principal outstanding			25,000			10,000
End of term charge			1,463			1,170
Total principal outstanding and end of term charge			26,463			11,170
Unamortized discount and issuance costs			(1,499	)		(1,629	)
Loan Payable	$		24,964		$	9,541

Loan Payable - current	$		—		$	—
Loan Payable - noncurrent			24,964			9,541
Loan Payable	$		24,964		$	9,541

The Company estimated the fair value of the warrant liability as of December 31, 2023 using probability assumptions of achieving the future milestones and using the Black-Scholes model based on the following key assumptions:


	Year Ended December 31,
	2023			2022
Expected term (in years)		5.5			6.5
Expected volatility		83.22	%		77.29	%
Risk-free interest rate		3.84	%		4.18	%
Expected dividend yield		0.00	%		0.00	%

Stock-based awards (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of assumptions used to determine grant-date fair value of stock options granted

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees, directors and consultants as follows, presented on a weighted average basis:


	Year Ended December 31,
	2023			2022			2021
Expected term (in years)		5.95			5.30			5.77
Expected volatility		81.89	%		74.59	%		72.17	%
Weighted average risk-free interest rate		4.19	%		2.71	%		1.19	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Summary of stock option activity

The following table summarizes the Company’s stock option activity since December 31, 2022:


				Weighted-		Weighted-
				Average		Average		Aggregate
				Exercise		remaining		Intrinsic
	Number			Price per		contractual		Value
	of Options			Share		term (years)		(000's)
Balance outstanding, December 31, 2022		5,780,004		$	18.88		7.80	$	207,611
Options granted		1,720,882		$	28.29
Options exercised		(593,959	)	$	5.50
Options cancelled		(6,950	)	$	49.74
Balance outstanding, December 31, 2023		6,899,977		$	22.35		7.67	$	35,133
Vested and expected to vest, December 31, 2023		6,899,977		$	22.35		7.67	$	35,133
Exercisable, December 31, 2023		4,126,549		$	18.32		6.69	$	28,508

Summary of stock-based compensation expense

The following table summarizes the Company’s stock-based compensation expense during the years ended December 31, 2023, 2022 and 2021:


	Year Ended December 31,
	2023		2022		2021
Classified within research and development expense	$	7,579	$	8,096	$	3,054
Classified within general and administrative expense		13,918		15,147		7,000
Total stock-based compensation expense	$	21,497	$	23,243	$	10,054

Summary of restricted stock activity

The following table summarizes the Company’s RSUs activity since December 31, 2022:


				Weighted-		Weighted-
				Average		Average		Aggregate
				Grant Date		remaining		Intrinsic
	Underlying			Fair Value per		contractual		Value
	shares			Share		term (years)		(000's)
Balance outstanding, December 31, 2022		129,131		$	42.95		2.07	$	7,076
Granted		281,462		$	24.03
Vested		(38,641	)	$	43.94
Cancelled or forfeited		—		$	—
Balance outstanding, December 31, 2023		371,952		$	28.53		1.98	$	8,685

Fair value of financial assets and liabilities - Textual (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers into level 3 Assets	$ 0	$ 0
Transfers out of level 3 Assets	0	0
Transfers into level 3 liabilities	0	0
Transfers out of level 3 liabilities	$ 0	$ 0

Amgen license agreement

12 Months Ended

Dec. 31, 2023

Amgen license agreement

Amgen license agreement

9. Amgen license agreement

In June 2018, the Company entered into a license agreement (the “Amgen Agreement”) with Amgen, Inc. (“Amgen”) pursuant to which the Company was granted an exclusive license to certain patents and intellectual property related to a long-acting FGF21 analog in order to commercially develop, manufacture, use and distribute FGF21 as a treatment for MASH and other serious metabolic diseases. The Amgen Agreement provides the Company with exclusive global rights to the licensed products and the right to grant sublicenses that cover EFX to third parties.

In exchange for these rights, the Company made an upfront payment of $5,000 and issued 2,653,333 shares of Series A Preferred Stock with a fair value of $1,353 to Amgen. Amgen was also entitled to maintain a 10% ownership interest of the outstanding shares of the Company’s common stock, on a fully diluted and converted basis, through the second closing of the Company’s Series A Preferred Stock financing. In November 2018, in connection with the second

closing of the Company’s Series A Preferred Stock financing, the Company issued 3,205,128 shares of Series A Preferred Stock to Amgen for a total value of $7,404, satisfying its anti-dilution obligation under the Amgen Agreement.

Under the Amgen Agreement, the Company made a milestone payment in the third quarter of 2019 of $2,500 in connection with dosing the first patient in the BALANCED study, a second milestone payment of $7,500 was paid in December 2023 with dosing the first patient in our Phase 3 SYNCHRONY program, and is obligated to pay Amgen up to $30,000 in connection with marketing approvals, and aggregate milestone payments of up to $75,000 upon the achievement of specified commercial milestones for all products licensed under the Amgen Agreement.

Under the Amgen Agreement, the Company is obligated to pay Amgen tiered royalties ranging from a low to high single-digit percentages on annual net sales of the licensed products, beginning on the first commercial sale of such licensed products in each country and expiring on a country-by-country basis on the latest of (i) the expiration of the last valid patent claim covering such licensed products in such country, (ii) the loss of regulatory exclusivity in such country, and (iii) ten years after the first commercial sale of such licensed product in such country. The royalty payments are subject to reduction under specified conditions set forth in the Amgen Agreement.

The Company is solely responsible for all development, manufacturing, and commercial activities and costs of the licensed products, including clinical studies or other tests necessary to support the use of a licensed product. The Company is also responsible for costs related to the filing, prosecution and maintenance of the licensed patent rights.

The Amgen Agreement will remain in effect until the expiration of the royalty term in all countries for all licensed products. The Amgen Agreement may be terminated by either party with at least 90 days' notice in the event of material breach by the other party that remains uncured for 90 days, by either party for insolvency or bankruptcy of the other party and immediately by Amgen if the Company challenges the licensed patents. The Company may also terminate the Amgen Agreement with 90 days' written notice for discretionary reasons such as scientific, technical, regulatory or commercial issues, as defined in the Amgen Agreement.

During the year ended December 31, 2023, the Company recorded $7,500 in research and development expense under the Amgen license in connection with dosing the first patient in the Phase 3 SYNCHRONY program. There was no expense recorded during the years ended December 31, 2022 and 2021.

Loan Payable and Warrant Liability (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Future principal Debt Payments on Loan Payable

Future principal debt payments on the currently outstanding loan payable as of December 31, 2023 and 2022 are as follows (in thousands):


		Year Ended December 31,
			2023			2022
2023	$		—		$	—
2024			—			1,710
2025			7,343			3,725
2026			16,118			4,169
2027			1,539			396
Total principal outstanding			25,000			10,000
End of term charge			1,463			1,170
Total principal outstanding and end of term charge			26,463			11,170
Unamortized discount and issuance costs			(1,499	)		(1,629	)
Loan Payable	$		24,964		$	9,541

Loan Payable - current	$		—		$	—
Loan Payable - noncurrent			24,964			9,541
Loan Payable	$		24,964		$	9,541

Schedule of Assumptions Used to Determine Estimated Fair Value of Warrant Liability


	Year Ended December 31,
	2023			2022
Expected term (in years)		5.5			6.5
Expected volatility		83.22	%		77.29	%
Risk-free interest rate		3.84	%		4.18	%
Expected dividend yield		0.00	%		0.00	%

Summary of significant accounting policies (Policies)	12 Months Ended
Summary of significant accounting policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Operating segment information	Operating segment information Operating segments are defined as components of an enterprise for which separate and discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company has one operating segment. The Company’s focus is the research and development of treatments for patients with serious metabolic diseases marked by high unmet medical need, including MASH, a disease without any approved therapies. The Company’s chief operating decision maker, its chief executive officer, manages the Company’s operations on a consolidated basis for the purpose of allocating resources.
Use of estimates	Use of estimates The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the recognition of research and development expenses, stock-based compensation expense, warrant liabilities and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Cash and cash equivalents	Cash and cash equivalents The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts.
Short and long-term marketable securities	Short and long-term marketable securities The Company invests in short and long-term marketable securities, primarily money market funds, commercial paper, U.S. treasury securities and corporate debt securities. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with high ratings from top rating agencies. The Company classifies its short and long-term marketable securities as available-for-sale securities and reports them at fair value in short and long-term marketable securities on the consolidated balance sheets with related unrealized gains and losses included within accumulated other comprehensive gain (loss) on the consolidated balance sheets. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income on the consolidated statements of operations and comprehensive loss. When the fair value is below the amortized cost of a marketable security, the Company reviews and determines whether the impairment is due to credit-related factors or noncredit-related factors. The credit-related impairment amount is recognized in other income on the consolidated statements of operations and comprehensive loss, with a corresponding allowance for credit losses account in the consolidated balance sheet. Subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations. There were no credit losses recorded during the years ended December 31, 2023, 2022 and 2021.
Restricted cash	Restricted cash As of December 31, 2022, the Company was required to maintain a separate cash balance of $108 for the benefit of the landlord in connection with the Company’s Gateway office space lease in South San Francisco, California (the “Gateway Lease”), which is classified within other assets (non-current) on the consolidated balance sheets (see Note 12). The Company was not required to maintain a separate cash balance for the benefit of the landlord as of December 31, 2023.
Concentrations of credit risk	Concentrations of credit risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, short and long-term marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash investments in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. At December 31, 2023, all of the Company's cash, cash equivalents, short and long-term investments were held at four accredited financial institutions. As of December 31, 2022, the Company held cash deposits at Silicon Valley Bank ("SVB") in excess of government insured limits. On March 10, 2023, SVB was closed by the California Department of Financial Protection and Innovation, and the Federal Deposit Insurance Corporation (“FDIC”) was appointed as receiver. No losses were incurred by the Company on deposits that were held at SVB. Management believes that the Company is not currently exposed to significant credit risk as the vast majority of the Company’s deposits were either owned directly by the Company and held in custody at a third-party financial institution or, subsequent to March 10, 2023, have been transferred to a third-party financial institution. On March 27, 2023, SVB was acquired by First-Citizen BancShares, Inc ("First-Citizen"). As of December 31, 2023, the Company did not have any significant deposits on account at or relationships with SVB or First-Citizen.
Leases	Leases The Company determines whether an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether the Company has the right to control the identified asset. Right-of-use, or ROU, assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and are further adjusted by any lease payments made prior to or on lease commencement, lease incentives received and initial direct costs incurred, as applicable. The Company has elected to not recognize leases with a lease term of one year or less on its balance sheet. Operating lease costs included in the measurement of the lease are recognized on a straight-line basis over the lease term. Variable lease costs are expensed as incurred as an operating expense. The Company determines the lease classification and the present value of future lease payments at the time of the lease commencement using an incremental borrowing rate that it estimates based upon the Company’s credit risk and term of the lease. The interest rate implicit in lease contracts has not historically been readily determinable and the Company must therefore use the appropriate incremental borrowing rate to measure its leases. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating.
Research and development costs	Research and development costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, third-party license fees and external costs including fees paid to consultants, contract manufacturing organizations, or CMOs, and clinical research organizations, or CROs, in connection with drug product manufacturing, nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered. Foreign currency transaction gains and losses related to the purchase of contract manufacturing services are included as a component of research and development expense. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. Accrued and prepaid research and development expenses
Accrued and prepaid research and development expenses	The Company has entered into various research and development and other agreements with commercial firms, researchers and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses are incurred. The Company makes estimates of accrued and prepaid research and development expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known at that time. When evaluating the adequacy of the accrued liabilities and the appropriateness of the prepaid expenses, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ materially from the Company's estimates.
Stock-based compensation	Stock-based compensation The Company makes stock-based awards from its stock compensation plans (see Note 8). The Company measures all stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company recognizes stock-based compensation expense for awards that contain performance-based conditions using the accelerated attribution method when management determines it is probable that the performance condition will be satisfied. The Company accounts for forfeitures as they occur. Stock-based compensation for restricted stock units is measured based on the market closing price of our common stock on the grant date. Stock-based compensation expense is recognized on a straight-line basis over the requisite service period, generally four years. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the option, the risk-free interest rate for a period that approximates the expected term of the option, and the Company's expected dividend yield. The Company currently estimates its share price volatility using a combination weighting of the historical volatility of publicly traded peer companies and the volatility of its traded share price and expects to continue to do so until mid-2025. The expected term of the Company's stock options has been determined utilizing the "simplified" method for awards that qualify as "plain-vanilla" options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. The fair value of each common stock award is estimated on the date of grant based on the fair value of the Company's common stock on that same date. Compensation expense for purchases under the Employee Stock Purchase Plan is recognized based on the fair value of the common stock estimated based on the closing price of our common stock as reported on the date of offering, less the purchase discount percentage provided for in the plan. The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified.
Loan Payable	Loan Payable Loan Payable represents the Loan and Security Agreement, dated June 15, 2022 (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), which the Company has accounted for as a debt financing arrangement. Interest expense is accrued using the effective interest rate method over the estimated period the loan will be repaid. Loan issuance costs have been recorded as a debt discount in the consolidated balance sheets and are being amortized and recorded as interest expense throughout the life of the Loan Agreement using the effective interest rate method. The Company considered whether there were any embedded features in the Loan Agreement that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification ("ASC") Topic 815, Derivatives and Hedging.
Warrant Liabilities	Warrant Liabilities The Company accounts for warrants anticipated to be issued in the future under the Loan Agreement as liabilities and measures them at fair value using the Black-Scholes valuation model. The warrants are subject to remeasurement at each prospective balance sheet date, with any changes in the fair value recorded in the consolidated statements of operations.
Income taxes	Income taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company's tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Net loss per share	Net loss per share Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the Company’s net loss.
Comprehensive loss	Comprehensive loss Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains and losses on its short and long-term marketable securities.
Recently adopted accounting pronouncements	Recently adopted accounting pronouncements As of December 31, 2023, and for the year then ended, there were no recently adopted accounting standards that had a material impact on the Company’s consolidated financial statements. There were no recently issued accounting standards not yet adopted which would have a material effect on the Company’s consolidated financial statements.
Recently Issued Accounting Standards Not Yet Adopted	Recently Issued Accounting Standards Not Yet Adopted In December 2023, the Financial Accounting Standards Board (“FASB”), issued Accounting Standards Update (“ASU”) No. 2023-09, Income Taxes (Topic 740), Improvements to Income Tax Disclosures, to enhance the transparency and decision usefulness of income tax disclosures. The enhancement will provide information to better assess how an entity’s operations and related tax risks and tax planning and operational opportunities affect its tax rate and prospects for future cash flows. Investors currently rely on the rate reconciliation table and other disclosures, including total income taxes paid, to evaluate income tax risks and opportunities. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-09 will have on its consolidated financial statements and related disclosures. In November 2023, the FASB, issued ASU No. 2023-07, Segment Reporting (Topic 280), Improvements to Reportable Segment Disclosures, to improve reportable segment disclosure requirements. The amendment introduced new requirements to disclose significant segment expenses regularly provided to the chief operating decision maker (“CODM”) and extend certain annual disclosures to interim periods. Entities with a single reportable segment must apply ASC 280 in its entirety, are permitted to report more than one measure of segment profit or or loss under certain conditions and are required to disclose the title and position of the CODM. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years after December 15, 2024 and early adoption is permitted. The Company is currently evaluating the impact ASU No. 2023-07 will have on its consolidated financial statements and related disclosures.

Stockholder's equity (deficit)

12 Months Ended

Dec. 31, 2023

Stockholders' Equity Note [Abstract]

Stockholder's equity (deficit)

7. Stockholder’s equity (deficit)

Common stock

As of December 31, 2023 and 2022, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 shares of $0.0001 par value common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. The holders of common stock, voting exclusively and as a separate class, have the exclusive right to vote for the election of directors of the Company. Common stockholders are entitled to receive dividends, as may be declared by the board of directors. Through December 31, 2023, no cash dividends had been declared or paid.

On June 24, 2019, the Company completed its IPO at which time the Company issued 6,612,500 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 862,500 additional shares of common stock, at a public offering price of $16.00 per share. The Company received $98,394, net of underwriting discounts and commissions, but before deducting offering costs paid by the Company, which were $2,942. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 21,056,136 shares of common stock.

On July 10, 2020, the Company completed a follow-on public offering at which time the Company issued 6,012,390 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 784,224 additional shares of common stock, at a public offering price of $36.00 per share. The Company received $203,460 net of underwriting discounts and commissions, but before deducting offering costs paid by the Company.

On May 18, 2021, the Company filed a Form S-3 Registration Statement and the accompanying prospectus activating an At-The-Market ("ATM"), facility by entering into a sales agreement with J.P. Morgan Securities LLC, relating to shares of the Company’s common stock offered. Pursuant to the terms of the sales agreement, the Company may offer and sell shares of common stock, having an aggregate price of up to $100,000, from time to time. The Company reserved 5,000,000 shares of common stock related to the ATM offering. In March 2023, the Company terminated the sales agreement with J.P. Morgan Securities LLC and separately entered into a sales agreement with Jefferies LLC (the "Sales Agreement"). Pursuant to the Sales Agreement, the Company filed a prospectus supplement on March 17, 2023, under which the Company may offer and sell shares of common stock, having an aggregate value of up to $200,000. In April and May 2023, the Company sold 3,006,052 shares of common stock under the Sales Agreement, at an average price of $42.38 per share. The Company received net proceeds of $123,824, after deducting sales agent commissions and issuance costs incurred by the Company of approximately $3,578.

On June 15, 2022, the Company entered into a securities purchase agreement for the sale of 2,525,252 shares of the Company's common stock to Pfizer Inc. at $9.90 per share in a registered direct offering conducted without an underwriter or placement agent and pursuant to the Company’s effective shelf registration statement on Form S-3ASR and a related prospectus supplement filed with the SEC. The offering closed on June 17, 2022 for net proceeds of $24,647, after deducting offering costs paid by the Company.

On September 19, 2022, the Company completed a follow-on public offering at which time the Company issued 8,846,154 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 1,153,846 additional shares of common stock, at a public offering price of $26.00 per share. The Company received $216,200 net of underwriting discounts and commissions of $13,800, but before deducting offering costs incurred by the Company.

On May 16, 2023, the Company entered into an underwriting agreement (the "Underwriting Agreement") with Jefferies LLC, ("Jefferies"), as a representative of the several underwriters, pursuant to which the Company agreed to issue and sell 5,238,500 shares of the Company's common stock at $42.00 per share in a registered direct offering pursuant to the Company’s effective shelf registration statement on Form S-3ASR and a related prospectus supplement

filed with the SEC. The offering closed on May 16, 2023. The Company received net proceeds of $210,956, after deducting underwriters commissions and offering costs incurred by the Company of approximately $9,061.

As of December 31, 2023 and 2022, there were 55,754,445 and 46,865,206 shares of common stock issued and outstanding, respectively.

The following shares of common stock were reserved for issuance as follows:


	December 31, 2023		December 31, 2022
Options outstanding under the 2018 Stock Option and Grant Plan		1,114,189		1,633,173
Options outstanding under the 2019 Stock Option and Incentive Plan		5,785,788		4,146,831
Restricted stock units outstanding under the 2019 Stock Option and Incentive Plan		371,952		129,131
Warrants to purchase common stock associated with Loan Agreement		45,898		36,718
Options available for future grant		1,917,356		2,038,142
Warrants available for future grant		137,700		146,880
Common stock available for ATM program		2,708,234		5,000,000
2019 Employee Stock Purchase Plan		1,586,224		1,187,508
		13,667,341		14,318,383

Undesignated preferred stock

The Company’s fourth amended and restated certificate of incorporation authorizes the Company to issue up to 10,000,000 shares of undesignated preferred stock, par value $0.0001 per share. There were no undesignated preferred shares issued or outstanding as of December 31, 2023.

Warrants Associated with Loan Agreement

In connection with the entry into the Loan Agreement, the Company issued to Hercules warrants to purchase shares of the Company’s common stock. The amount of shares that may be purchased for the Warrants will not exceed 1.5% multiplied by the greater of Tranche I and the aggregate original amount of the term loan advances, divided by the exercise price of the Warrants. Upon execution of the Loan Agreement on June 15, 2022, the Company issued 36,718 warrants to purchase shares of the Company’s common stock and recorded the initial warrants at their relative fair value in shareholder's equity. In March of 2023, the Company issued an additional 9,180 warrants to purchase shares of the Company’s common stock to Hercules in connection with an additional $15,000 borrowing (see Note 6).

On February 28, 2024 the Company amended the Hercules Loan Agreement to increase the total amount of borrowings available to $150,000 and to change the conditions under which the remaining borrowings will become available. In connection with this amendment, the Company borrowed an additional $10,000 under the loan facility. In connection with the $10,000 borrowed at the time of the amendment, the Company will issue 18,359 additional warrants to purchase shares of the Company’s common stock to Hercules (see Notes 6 and 13).

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Loan Payable and Warrant Liability - Schedule of Future principal Debt Payments on Loan Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Long-Term Debt, Fiscal Year Maturity [Abstract]
2024		$ 1,710
2025	$ 7,343	3,725
2026	16,118	4,169
2027	1,539	396
Total principal outstanding	25,000	10,000
End of term charge	1,463	1,170
Total principal outstanding and end of term charge	26,463	11,170
Unamortized discount and issuance costs	(1,499)	(1,629)
Loan Payable	24,964	9,541
Loan Payable - noncurrent	$ 24,964	$ 9,541

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Statement of Stockholders' Equity [Abstract]
Net issuance costs and underwriting fees	$ 13,800

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($)	Total	ATM Offering	Direct Offering	Common Stock	Common Stock ATM Offering	Common Stock Direct Offering	Additional Paid-In-Capital	Additional Paid-In-Capital ATM Offering	Additional Paid-In-Capital Direct Offering	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance at beginning at Dec. 31, 2020	$ 258,712,000			$ 4,000			$ 468,238,000			$ (3,000)	$ (209,527,000)
Balance at beginning (in shares) at Dec. 31, 2020				34,741,649
Exercise of stock options	750,000						750,000
Exercise of stock options (in shares)				140,128
Vesting of restricted stock	21,000						21,000
Issuance of common stock pursuant to ESPP purchases	373,000						373,000
Issuance of common stock pursuant to ESPP purchases (in shares)				18,950
Stock-based compensation expense	10,054,000						10,054,000
Net unrealized gain (loss) on marketable securities	(24,000)									(24,000)
Net loss	(100,777,000)										(100,777,000)
Balance at ending at Dec. 31, 2021	169,109,000			$ 4,000			479,436,000			(27,000)	(310,304,000)
Balance at ending (in shares) at Dec. 31, 2021				34,900,727
Exercise of stock options	5,238,000						5,238,000
Exercise of stock options (in shares)				559,145
Issuance of common stock pursuant to ESPP purchases	280,000						280,000
Issuance of common stock pursuant to ESPP purchases (in shares)				33,928
Issuance of common stock, net of issuance costs	24,647,000						24,647,000
Issuance of common stock (in shares)				2,525,252
Additional warrants to purchase shares	227,000						227,000
Issuance of common stock upon closing of follow-on public offering, net of issuance costs and underwriting fees (shares)				8,846,154
Issuance of common stock upon closing of follow-on public offering, net of issuance costs and underwriting fees	215,787,000			$ 1,000			215,786,000
Stock-based compensation expense	23,243,000						23,243,000
Net unrealized gain (loss) on marketable securities	64,000									64,000
Net loss	(112,033,000)										(112,033,000)
Balance at ending at Dec. 31, 2022	326,562,000			$ 5,000			748,857,000			37,000	(422,337,000)
Balance at ending (in shares) at Dec. 31, 2022				46,865,206
Exercise of stock options	$ 3,267,000						3,267,000
Exercise of stock options (in shares)	593,959			593,959
Common stock issued for vested restricted stock units, Shares				38,641
Issuance of common stock pursuant to ESPP purchases	$ 396,000						396,000
Issuance of common stock pursuant to ESPP purchases (in shares)				12,087
Issuance of common stock, net of issuance costs		$ 123,824,000	$ 210,956,000			$ 1,000		$ 123,824,000	$ 210,955,000
Issuance of common stock (in shares)					3,006,052	5,238,500
Additional warrants to purchase shares	330,000						330,000
Stock-based compensation expense	21,497,000						21,497,000
Net unrealized gain (loss) on marketable securities	233,000									233,000
Net loss	(151,759,000)										(151,759,000)
Balance at ending at Dec. 31, 2023	$ 535,306,000			$ 6,000			$ 1,109,126,000			$ 270,000	$ (574,096,000)
Balance at ending (in shares) at Dec. 31, 2023				55,754,445

Income taxes - Current income tax provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred income tax benefit:
Federal	$ 40,292	$ 27,269	$ 23,352
State	28,079	14,568	7,274
Total deferred income tax benefit	68,371	41,837	30,626
Change in deferred tax asset valuation allowance	$ (68,371)	$ (41,837)	$ (30,626)

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	55,754,445	46,865,206
Common stock, shares outstanding	55,754,445	46,865,206

Short and long-term marketable securities

12 Months Ended

Dec. 31, 2023

Short-term marketable securities

Short and long-term marketable securities

4. Short and long-term marketable securities

The following is a summary of short and long-term marketable securities as of December 31, 2023 and 2022:


	December 31, 2023
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Credit losses		Fair value
Money market funds	$	206,879	$	—	$	—		$	—	$	206,879
U.S. Treasury securities		117,058		255		(6	)		—		117,307
U.S. Government agency securities		133,279		78		(60	)		—		133,297
Commercial paper		68,707		10		(9	)		—		68,708
Corporate debt securities		15,773		1		—			—		15,774
	$	541,696	$	344	$	(75	)	$	—	$	541,965

Cash equivalents										$	206,879
Short-term marketable securities											315,803
Long-term marketable securities											19,283
										$	541,965

	December 31, 2022
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Credit losses		Fair value
Money market funds	$	137,286	$	—	$	—		$	—	$	137,286
U.S. Treasury securities		58,698		23		—			—		58,721
Corporate debt securities		5,478		—		(2	)		—		5,476
U.S. Government agency securities		62,939		15		—			—		62,954
Commercial paper		27,739		—		—			—		27,739
	$	292,140	$	38	$	(2	)	$	—	$	292,176

Cash equivalents										$	190,500
Short-term marketable securities											101,676
										$	292,176

The following table presents the contractual maturities of our short and long-term marketable securities as of December 31, 2023 and December 31, 2022.

Commitments and contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and contingencies

12. Commitments and contingencies

Operating lease

In February 2020, the Company entered into a seven-year agreement to occupy 6,647 square feet of office space in South San Francisco, California. The lease commenced on July 10, 2020 when the Company took occupancy of the leased space and the lease was determined to be operating classified. Under the agreement, the Company is required to make approximately $2,300 in total minimum payments during the term. The Company is also required to pay its proportionate share of building operating and tax costs after the first year under lease which are not included in the measurement of the lease and treated as variable lease cost and expensed when incurred.

As of December 31, 2023, maturities of the Company’s operating lease liability was as follows:


2024	$	331
2025		341
2026		351
2027		208
Total future minimum lease payments		1,231
Less imputed interest		(152	)
Present value of operating lease liabilities	$	1,079

As of December 31, 2023, the total lease liability was $1,079, of which $819 was noncurrent and $260 was short-term and classified within “Accrued expenses and other current liabilities” on the consolidated balance sheet.

For the years ended December 31, 2023, 2022 and 2021, the components of operating lease cost were as follows:


		Year Ended December 31,
			2023				2022				2021
Lease cost:	Statement of Operations Classification:
Operating lease cost	General and administrative expense	$		324		$		324		$		324
Short-term lease cost	General and administrative expense			161				58				—
Variable operating lease cost	General and administrative expense			37				58				17
Total operating lease cost		$		522		$		440		$		341

Other information:
Cash paid for amounts included in the measurement of operating lease liability		$		321		$		312		$		303
Weighted average remaining lease term (years)				3.6				4.6				5.6
Weighted average discount rate				7.6	%			7.6	%			7.6	%

Research and manufacturing and other commitments

The Company has entered into agreements with contract research organizations and contract manufacturing organizations to provide services in connection with its nonclinical studies and clinical trials and to manufacture clinical development materials. As of December 31, 2023, the Company had non-cancelable purchase and other commitments under these agreements totaling $30,878.

Indemnification agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not currently aware of any indemnification claims and has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2023.

Legal proceedings

The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2023	Feb. 23, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2023
Entity File Number	001-38944
Entity Registrant Name	Akero Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-5266573
Entity Address, Address Line One	601 Gateway Boulevard, Suite 350
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
Document Financial Statement Error Correction [Flag]	false
City Area Code	650
Local Phone Number	487‑6488
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	AKRO
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Common Stock, Shares Outstanding		56,297,528
Entity Public Float			$ 2,517,511,353
Entity Central Index Key	0001744659
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
Auditor Name	Deloitte & Touche LLP
Auditor Firm ID	34
Auditor Location	Morristown, NJ
Documents Incorporated by Reference [Text Block]	Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2024 annual meeting of shareholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2023. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Commitments and contingencies - Maturities Of Operating Leases (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract]
2024	$ 331
2025	341
2026	351
2027	208
Total future minimum lease payments	1,231
Less imputed interest	(152)
Present value of operating lease liabilities	$ 1,079

Stockholder's equity (deficit) - Common stock (Details)									1 Months Ended		12 Months Ended
Stockholder's equity (deficit) - Common stock (Details)	May 16, 2023 USD ($) $ / shares shares	Mar. 17, 2023 USD ($)	Sep. 19, 2022 USD ($) $ / shares shares	Jun. 17, 2022 USD ($)	Jun. 15, 2022 $ / shares shares	May 18, 2021 USD ($) shares	Jul. 10, 2020 USD ($) $ / shares shares	Jun. 24, 2019 USD ($) $ / shares shares	May 31, 2023 $ / shares shares	Apr. 30, 2023 $ / shares shares	Dec. 31, 2023 USD ($) Vote $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Jun. 18, 2019 shares
Class of Stock [Line Items]
Common stock, shares authorized											150,000,000	150,000,000
Common stock, par value (in dollars per share) \| $ / shares											$ 0.0001	$ 0.0001
Number of votes per share \| Vote											1
Cash dividend declared \| $ / shares											$ 0
Cash dividend paid \| $ / shares											$ 0
Net proceeds from the sales of common stock in equity offerings \| $											$ 818,900,000
Share Issued value under agreement \| $												$ 24,647,000
Common stock, shares issued											55,754,445	46,865,206
Common stock, shares outstanding											55,754,445	46,865,206
Common stock were reserved for issuance
Options available for future grant											13,667,341	14,318,383
Jeffries
Class of Stock [Line Items]
Net proceeds from the sales of common stock in equity offerings \| $	$ 210,956,000
Offering costs \| $	$ 9,061,000
Common stock, shares issued	5,238,500
Sale of stock under agreement	5,238,500
Sale of stock, price per share \| $ / shares	$ 42
Employee Stock Option
Common stock were reserved for issuance
Options available for future grant											1,917,356	2,038,142
Common stock Available under ATM Offering
Class of Stock [Line Items]
Net proceeds from the sales of common stock in equity offerings \| $				$ 24,647,000							$ 123,824,000
Offering costs \| $											$ 3,578,000
Sale of stock under agreement									3,006,052	3,006,052
Sale of stock, price per share \| $ / shares									$ 42.38	$ 42.38
Common stock were reserved for issuance
Options available for future grant						5,000,000					2,708,234	5,000,000
Common stock Available under ATM Offering \| Pfizer Inc
Class of Stock [Line Items]
Sale of stock under agreement					2,525,252
Sale of stock, price per share \| $ / shares					$ 9.9
Warrants to Purchase Common Stock
Common stock were reserved for issuance
Options available for future grant											45,898	36,718
Warrants Available for Future Grant
Common stock were reserved for issuance
Options available for future grant											137,700	146,880
2018 Stock option and grant plan
Common stock were reserved for issuance
Options available for future grant											1,114,189	1,633,173	107,635
2019 Stock Option and Incentive plan
Common stock were reserved for issuance
Options available for future grant											5,785,788	4,146,831
2019 Stock Option and Incentive plan \| Restricted Stock Units
Common stock were reserved for issuance
Options available for future grant											371,952	129,131
2019 Employee Stock Purchase Plan
Common stock were reserved for issuance
Options available for future grant											1,586,224	1,187,508
Maximum \| Common stock Available under ATM Offering
Class of Stock [Line Items]
Share Issued value under agreement \| $		$ 200,000				$ 100,000
IPO
Class of Stock [Line Items]
Public offering price \| $ / shares								$ 16
Net proceeds from the sales of common stock in equity offerings \| $								$ 98,394,000
Offering costs \| $								$ 2,942,000
Number of shares converted								21,056,136
Common stock, shares issued								6,612,500
Follow Up Public Offering
Class of Stock [Line Items]
Share Issued under agreement			8,846,154				6,012,390
Public offering price \| $ / shares			$ 26				$ 36
Net proceeds from the sales of common stock in equity offerings \| $			$ 216,200,000				$ 203,460,000
Offering costs \| $			$ 13,800,000
Over allotment \| Maximum
Class of Stock [Line Items]
Share Issued under agreement			1,153,846				784,224
Common stock, shares issued								862,500

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of current and deferred tax provision

A summary of the Company’s current and deferred tax provision is as follows:


	Year Ended December 31,
	2023			2022			2021
Current income tax provision:
Federal	$	—		$	—		$	—
State		—			—			—
Total current income tax provision		—			—			—
Deferred income tax benefit:
Federal		40,292			27,269			23,352
State		28,079			14,568			7,274
Total deferred income tax benefit		68,371			41,837			30,626
Change in deferred tax asset valuation allowance		(68,371	)		(41,837	)		(30,626	)
Total provision for income taxes	$	—		$	—		$	—

Schedule of reconciliation of the U.S. federal statutory income tax

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2023				2022				2021
Federal statutory income tax rate		21.0		%		21.0		%		21.0		%
State income taxes, net of federal benefit		18.5				13.0				7.2
Research and development tax credits		2.4				2.4				2.0
Other permanent differences		2.6				0.8				(0.1	)
Change in deferred tax asset valuation allowance		(44.5	)			(37.2	)			(30.1	)
Effect of Section 382 limitation		-				-				-
Effective income tax rate		-		%		-		%		-		%

Schedule of Net deferred tax assets

Net deferred tax assets as of December 31, 2023 and 2022 consisted of the following:


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carry forwards	$	88,219		$	68,450
Research and development tax credit carry forwards		12,846			7,704
License fees		5,545			3,355
Stock based compensation		14,286			8,974
Capitalized research and experimentation costs		58,610			20,803
Accruals, reserves and other		242			191
		179,748			109,477
Valuation allowance		(177,061	)		(108,690	)
Net deferred tax assets	$	2,687			787

Deferred tax liabilities:
Prepaid expenses		(2,687	)		(787	)
Net deferred tax liabilities	$	(2,687	)		(787	)

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued expenses and other current liabilities
Accrued external research and development expenses	$ 10,041	$ 9,789
Accrued employee compensation and benefits	1,296	804
Accrued legal and professional fees	231	197
Short-term lease liability and other	522	325
Total accrued expenses and other current liabilities	$ 12,090	$ 11,115

Stockholder's equity (deficit) - Warrants Associated with Loan Agreement (Details) - USD ($)			3 Months Ended	12 Months Ended
	Feb. 28, 2024	Jun. 15, 2022	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Mar. 10, 2023
Class of Stock [Line Items]
Proceeds from term loan				$ 15,000,000	$ 10,000,000
Loan Agreement
Class of Stock [Line Items]
Issued warrants to purchase shares of common stock				36,718
Hercules Capital Inc and Hercules Private Global Venture Growth Fund I L.P.
Class of Stock [Line Items]
Maximum percentage of warrants purchased				1.50%
Issued warrants to purchase shares of common stock		36,718	9,180
Hercules
Class of Stock [Line Items]
Issued warrants to purchase shares of common stock						9,180
Hercules \| Loan Agreement
Class of Stock [Line Items]
Proceeds from term loan			$ 15,000,000
Hercules \| Loan Agreement \| Term Loan
Class of Stock [Line Items]
Maximum borrowing capacity		$ 100,000,000
Proceeds from term loan		$ 10,000,000
Hercules \| Loan Agreement \| Term Loan \| Subsequent Event
Class of Stock [Line Items]
Issued warrants to purchase shares of common stock	18,359
Maximum borrowing capacity	$ 150,000,000
Proceeds from term loan	$ 10,000,000

Summary of significant accounting policies - Restricted cash (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Accounting Policies [Abstract]
Separate cash balance for the landlord	$ 108

Stock-based awards - Stock option valuation (Details)	12 Months Ended
Stock-based awards - Stock option valuation (Details)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assumptions to determine grant-date fair value of stock options granted
Expected term (in years)	5 years 11 months 12 days	5 years 3 months 18 days	5 years 9 months 7 days
Expected volatility	81.89%	74.59%	72.17%
Weighted average risk-free interest rate	4.19%	2.71%	1.19%
Expected dividend yield	0.00%	0.00%	0.00%

Net loss per share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net loss	$ (151,759)	$ (112,033)	$ (100,777)
Denominator:
Weighted average common shares outstanding, basic	52,568,159	38,984,772	34,827,385
Weighted average common shares outstanding, diluted	52,568,159	38,984,772	34,827,385
Net loss per share, basic	$ (2.89)	$ (2.87)	$ (2.89)
Net loss per share, diluted	$ (2.89)	$ (2.87)	$ (2.89)
Number of weighted average restricted common stock	0	0	8,127

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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-URI https://asc.fasb.org//1943274/2147482689/260-10-45-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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Reference 15: http://www.xbrl.org/2003/role/exampleRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 52
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-52

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-7

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Stock-based awards

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based awards

8. Stock-based awards

2018 Stock option and grant plan

The Company’s 2018 Stock Option and Grant Plan (the “2018 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards and other stock-based awards to employees, directors and consultants of the Company. The 2018 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

The total number of shares of common stock that could have been issued under the 2018 Plan was 3,071,960 shares, of which 107,635 shares remained available for grant on June 18, 2019, the date that the Company’s 2019 Stock Option and Incentive Plan (the “2019 Plan”) became effective. Upon the effectiveness of the 2019 Plan, the 107,635 remaining shares available under the 2018 Plan were transferred and became available for issuance under the 2019 Plan. Shares of common stock underlying outstanding awards under the 2018 Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) will be added to the shares of common stock available for issuance under the 2019 Plan.

2019 Stock option and incentive plan

The 2019 Plan was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 Plan became effective on June 18, 2019 and replaced the Company’s 2018 Plan on that date. The 2019 Plan allows the board of directors or the compensation committee of the board of directors to make equity-based incentive awards to the Company’s officers, employees, directors or other key persons (including consultants). The number of shares initially reserved for issuance under the 2019 Plan was 2,572,457, which included the 107,635 shares transferred from the 2018 Plan, and shall be cumulatively increased on each January 1 by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors. The 2019 Plan was increased by 1,396,029 shares on January 1, 2022 and by 1,874,608 shares on January 1, 2023.

The 2019 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. All incentive options granted to any person possessing more than 10% of the total combined voting power of all classes of shares may not have an exercise price of less than 110% of the fair market value of the common stock on the grant date. Stock options granted to employees, officers, members of the board of directors and consultants will typically vest over a four-year period.

Shares that are expired, terminated, surrendered or canceled under the 2019 Plan without having been fully exercised will be available for future awards.

2019 Employee stock purchase plan

The 2019 Employee Stock Purchase Plan (the “2019 ESPP”) was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 ESPP became effective on June 18, 2019, at which time 273,869 shares were reserved for issuance. The 2019 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2020 and each January 1 through January 1, 2029, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 410,803 shares or (iii) such number of shares as determined by the compensation committee. The 2019 ESPP was increased by 349,007 shares on January 1, 2022 and by 410,803 shares on January 1, 2023.

Stock option valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees, directors and consultants as follows, presented on a weighted average basis:


	Year Ended December 31,
	2023			2022			2021
Expected term (in years)		5.95			5.30			5.77
Expected volatility		81.89	%		74.59	%		72.17	%
Weighted average risk-free interest rate		4.19	%		2.71	%		1.19	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Stock options

The following table summarizes the Company’s stock option activity since December 31, 2022:


				Weighted-		Weighted-
				Average		Average		Aggregate
				Exercise		remaining		Intrinsic
	Number			Price per		contractual		Value
	of Options			Share		term (years)		(000's)
Balance outstanding, December 31, 2022		5,780,004		$	18.88		7.80	$	207,611
Options granted		1,720,882		$	28.29
Options exercised		(593,959	)	$	5.50
Options cancelled		(6,950	)	$	49.74
Balance outstanding, December 31, 2023		6,899,977		$	22.35		7.67	$	35,133
Vested and expected to vest, December 31, 2023		6,899,977		$	22.35		7.67	$	35,133
Exercisable, December 31, 2023		4,126,549		$	18.32		6.69	$	28,508

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

The weighted average grant-date fair value per share of stock options granted during the years ended December 31, 2023, 2022 and 2021 was $28.29, $28.76 and $13.98, respectively.

Awards with performance-based vesting conditions granted under the 2019 Plan

In December 2021, the Company granted 610,546 stock options to management at an exercise price of $21.10, which vest upon the achievement on or before December 31, 2022 of three pre-determined milestones regarding progress related to the HARMONY study, progress related to the SYMMETRY study, and progress related to availability of drug product for use in Phase 3 clinical trials. One-third of the options vest upon achievement of each of the milestones. In January 2022, the Company granted an additional 248,376 stock options to Company employees with the same performance-based milestones and vesting terms at an exercise price of $21.70. In September 2022, two of the three performance-based awards milestones were achieved and were deemed vested. In December 2022, the third portion of the performance-based awards milestones was achieved and was deemed vested. During the year ended December 31, 2022, the Company recognized $10,487 of related stock compensation expense, based upon management's estimates of the probabilities of the milestones being achieved and the fully vesting of the performance awards. During the year ended December 31, 2023, the Company did not have any outstanding performance awards or recognize any performance-based stock compensation expense.

Restricted Stock Units

The 2019 Plan allows for the grants of Restricted Stock Units (RSUs). Generally, the RSUs are subject to a four-year vesting period of which the Company has designated to vest on a quarterly basis over the remaining vesting term. In December 2022, the Company granted 129,131 RSUs to executive management with a total grant date fair value of $5,546. In 2023, the Company granted 281,462 RSUs to executive and non-executive employees with a total grant date fair value of $24.03.

The following table summarizes the Company’s RSUs activity since December 31, 2022:


				Weighted-		Weighted-
				Average		Average		Aggregate
				Grant Date		remaining		Intrinsic
	Underlying			Fair Value per		contractual		Value
	shares			Share		term (years)		(000's)
Balance outstanding, December 31, 2022		129,131		$	42.95		2.07	$	7,076
Granted		281,462		$	24.03
Vested		(38,641	)	$	43.94
Cancelled or forfeited		—		$	—
Balance outstanding, December 31, 2023		371,952		$	28.53		1.98	$	8,685

The weighted average grant-date fair value per share of RSUs granted during the years ended December 31, 2023 and 2022 was $24.03 and $42.95, respectively.

Stock-based compensation

The following table summarizes the Company’s stock-based compensation expense during the years ended December 31, 2023, 2022 and 2021:


	Year Ended December 31,
	2023		2022		2021
Classified within research and development expense	$	7,579	$	8,096	$	3,054
Classified within general and administrative expense		13,918		15,147		7,000
Total stock-based compensation expense	$	21,497	$	23,243	$	10,054

As of December 31, 2023, total unrecognized compensation cost related to unvested stock options and RSUs was $51,121 and 10,331, respectively. These unvested stock options and RSUs are expected to be recognized over a weighted average period of 2.87 years and 3.61 years respectively.

Net loss per share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Schedule of basic and diluted net loss per share attributable to common stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Year Ended December 31,
	2023			2022			2021
Numerator:
Net loss	$	(151,759	)	$	(112,033	)	$	(100,777	)
Denominator:
Weighted average common shares outstanding, basic and diluted		52,568,159			38,984,772			34,827,385
Net loss per share, basic and diluted	$	(2.89	)	$	(2.87	)	$	(2.89	)

Schedule of computation of diluted net loss per share attributable to common stockholders


	Years ended December 31,
	2023		2022		2021
Options to purchase common stock		6,899,977		5,780,004		5,221,094
Unvested restricted stock units		371,952		129,131		—
Warrants to purchase common stock		45,898		36,718		—
Warrants available for future grant		137,700		146,880		—
		7,455,527		6,092,733		5,221,094

Income taxes - Deferred tax (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets
Net operating loss carry forwards	$ 88,219	$ 68,450
Research and development tax credit carry forwards	12,846	7,704
License fees	5,545	3,355
Stock based compensation	14,286	8,974
Capitalized research and experimentation costs	58,610	20,803
Accruals, reserves and other	242	191
Total deferred tax assets	179,748	109,477
Valuation allowance	(177,061)	(108,690)	$ (66,853)
Net deferred tax assets	2,687	787
Deferred tax liabilities
Prepaid expenses	(2,687)	(787)
Net deferred tax liabilities	$ (2,687)	$ (787)

Accrued expenses and other current liabilities

12 Months Ended

Dec. 31, 2023

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities

5. Accrued expenses and other current liabilities

The following is a summary of accrued expenses and other current liabilities as of December 31, 2023 and 2022:


	December 31, 2023		December 31, 2022
Accrued external research and development expenses	$	10,041	$	9,789
Accrued employee compensation and benefits		1,296		804
Accrued legal and professional fees		231		197
Short-term lease liability and other		522		325
	$	12,090	$	11,115

Short and long-term marketable securities (Tables)

12 Months Ended

Dec. 31, 2023

Short-term marketable securities

Summary of short and long-term marketable securities

The following is a summary of short and long-term marketable securities as of December 31, 2023 and 2022:


	December 31, 2023
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Credit losses		Fair value
Money market funds	$	206,879	$	—	$	—		$	—	$	206,879
U.S. Treasury securities		117,058		255		(6	)		—		117,307
U.S. Government agency securities		133,279		78		(60	)		—		133,297
Commercial paper		68,707		10		(9	)		—		68,708
Corporate debt securities		15,773		1		—			—		15,774
	$	541,696	$	344	$	(75	)	$	—	$	541,965

Cash equivalents										$	206,879
Short-term marketable securities											315,803
Long-term marketable securities											19,283
										$	541,965

	December 31, 2022
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Credit losses		Fair value
Money market funds	$	137,286	$	—	$	—		$	—	$	137,286
U.S. Treasury securities		58,698		23		—			—		58,721
Corporate debt securities		5,478		—		(2	)		—		5,476
U.S. Government agency securities		62,939		15		—			—		62,954
Commercial paper		27,739		—		—			—		27,739
	$	292,140	$	38	$	(2	)	$	—	$	292,176

Cash equivalents										$	190,500
Short-term marketable securities											101,676
										$	292,176

Schedule of contractual maturities of short and long term marketable securities

The following table presents the contractual maturities of our short and long-term marketable securities as of December 31, 2023 and December 31, 2022.


	December 31, 2023		December 31, 2022
Due within one year	$	315,803	$	101,676
Due after one year through five years		19,283		—
Total	$	335,086	$	101,676

Income taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning	$ 2,110	$ 1,313	$ 644
Increases related to prior year tax positions	223	51	66
Increases related to current year tax positions	1,061	746	603
Balance at the ending	$ 3,394	$ 2,110	$ 1,313

Short and long-term marketable securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	$ 541,696	$ 292,140
Gross unrealized gains	344	38
Gross unrealized losses	(75)	(2)
Fair value	541,965	292,176
Cash equivalents	206,879	190,500
Short-term marketable securities	315,803	101,676
Long-term marketable securities	19,283
Total	541,965	292,176
Money market funds
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	206,879	137,286
Fair value	206,879	137,286
U.S. Treasury securities
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	117,058	58,698
Gross unrealized gains	255	23
Gross unrealized losses	(6)
Fair value	117,307	58,721
U.S. Government agency securities
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	133,279	62,939
Gross unrealized gains	78	15
Gross unrealized losses	(60)
Fair value	133,297	62,954
Commercial paper
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	68,707	27,739
Gross unrealized gains	10
Gross unrealized losses	(9)
Fair value	68,708	27,739
Corporate debt securities
Debt Securities, Available-for-Sale [Line Items]
Amortized cost	15,773	5,478
Gross unrealized gains	1
Gross unrealized losses		(2)
Fair value	$ 15,774	$ 5,476

Stockholder's equity (deficit) - Undesignated preferred stock and Restricted common stock (Details) - Undesignated Preferred Stock	Dec. 31, 2023 $ / shares shares
Class of Stock [Line Items]
Preferred stock, par value (in dollars per share) \| $ / shares	$ 0.0001
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0
Maximum
Class of Stock [Line Items]
Preferred stock, shares authorized	10,000,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 272
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483014/272-10-45-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 272
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482987/272-10-50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
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-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Publisher FASB
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
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-Subparagraph (b)
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (SX 210.5-02(27)(b))
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479886/946-10-S99-3

+ Details

Short and long-term marketable securities - Schedule of contractual maturities of short and long term marketable securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities [Abstract]
Due within one year	$ 315,803	$ 101,676
Due after one year through five years	19,283
Total	$ 335,086	$ 101,676

Fair value measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair value measurements

3. Fair value measurements

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The following is a summary of our financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022:


	December 31, 2023
	Total		Level 1		Level 2		Level 3
Money market funds	$	206,879	$	206,879	$	—	$	—
U.S. Treasury securities		117,307		117,307		—		—
U.S. Government agency securities		133,297		—		133,297		—
Commercial paper		68,708		—		68,708		—
Corporate debt securities		15,774		—		15,774		—
Total assets	$	541,965	$	324,186	$	217,779	$	—

Warrant liabilities	$	54	$	—	$	—	$	54
Total liabilities	$	54	$	—	$	—	$	54

	December 31, 2022
	Total		Level 1		Level 2		Level 3
Money market funds	$	137,286	$	137,286	$	—	$	—
U.S. Treasury securities		58,721		58,721		—		—
Corporate debt securities		5,476		—		5,476		—
U.S. Government agency securities		62,955		—		62,955		—
Commercial paper		27,738		—		27,738		—
Total assets	$	292,176	$	196,007	$	96,169	$	—

Warrant liabilities	$	305	$	—	$	—	$	305
Total liabilities	$	305	$	—	$	—	$	305

Corporate debt securities were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities. During the years ended December 31, 2023 and 2022, there were no transfers between Level 1, Level 2 and Level 3.

The Loan Payable is classified as a Level 3 liability. As of December 31, 2023, the carrying value of the Loan Payable, approximates its fair value. The Company estimated the fair value of the warrant liabilities using the Black-Scholes model based on key assumption and inputs (see Note 6). The Company utilizes a probability assessment to estimate the likelihood of vesting for the remaining Loan Agreement warrants and allocated the probability of occurrence percentage to the fair values calculated.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Net loss per share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net loss per share

11. Net loss per share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Year Ended December 31,
	2023			2022			2021
Numerator:
Net loss	$	(151,759	)	$	(112,033	)	$	(100,777	)
Denominator:
Weighted average common shares outstanding, basic and diluted		52,568,159			38,984,772			34,827,385
Net loss per share, basic and diluted	$	(2.89	)	$	(2.87	)	$	(2.89	)

The Company excluded 8,127 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share for the year 2021 because those shares had not vested. The were no restricted common stock for the years ended December 31, 2023 and 2022.

The Company’s potentially dilutive securities, which include stock options, warrants and unvested restricted common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce

the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	Years ended December 31,
	2023		2022		2021
Options to purchase common stock		6,899,977		5,780,004		5,221,094
Unvested restricted stock units		371,952		129,131		—
Warrants to purchase common stock		45,898		36,718		—
Warrants available for future grant		137,700		146,880		—
		7,455,527		6,092,733		5,221,094

Subsequent event

12 Months Ended

Dec. 31, 2023

Subsequent Events [Abstract]

Subsequent event

13. Subsequent event

The Company evaluated subsequent events through the issuance date.

On February 28, 2024, the Company amended the Hercules Loan Agreement to increase the total amount of borrowings available to $150,000 and to change the conditions under which the remaining borrowings will become available. In connection with this amendment, the Company borrowed an additional $10,000 under the loan facility. In connection with the $10,000 borrowed at the time of the amendment, the Company will issue 18,359 additional warrants to purchase shares of the Company’s common stock to Hercules (see Notes 6 and 7).

On February 14, 2024, the Company raised $10,603 in net proceeds through the sale of 500,000 shares of common stock under its ATM facility at an average price of $21.75 per share.

Loan Payable and Warrant Liability - Schedule of Assumptions Used to Determine Estimated Fair Value of Warrant Liability (Details)	Dec. 31, 2023	Dec. 31, 2022
Measurement Input, Expected Term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected term (in years)	5 years 6 months	6 years 6 months
Measurement Input, Price Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of the Warrants, Measurement input	0.8322	0.7729
Measurement Input, Risk-Free Interest Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of the Warrants, Measurement input	0.0384	0.0418
Measurement Input, Expected Dividend Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of the Warrants, Measurement input	0	0

Nature of the business and basis of presentation

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of the business and basis of presentation

1. Nature of the business and basis of presentation

Akero Therapeutics, Inc., together with its wholly owned subsidiary Akero Securities Corporation, (“Akero” or the “Company”) is a clinical-stage company dedicated to developing transformational treatments for patients with serious metabolic diseases marked by high unmet medical need, including metabolic dysfunction-associated steatohepatitis, or MASH, formerly known as non-alcoholic steatohepatitis, or NASH, a disease without any approved therapies. MASH is a severe form of metabolic dysfunction-associated steatotic liver disease, or MASLD, formerly known as nonalcoholic fatty liver disease, or NAFLD, characterized by inflammation and fibrosis in the liver that can progress to cirrhosis, liver failure, cancer and death. The Company's lead product candidate, efruxifermin, or EFX, is an analog of fibroblast growth factor 21, or FGF21, which is an endogenously expressed hormone that protects against cellular stress and regulates metabolism of lipids, carbohydrates and proteins throughout the body. The Company has initiated a Phase 3 program called SYNCHRONY, for which the first two of three planned clinical trials evaluating EFX have begun screening. EFX is also being evaluated in two ongoing, 96-week Phase 2b clinical trials in patients with biopsy-confirmed MASH: the HARMONY study in patients with pre-cirrhotic MASH (F2-F3 fibrosis) and the SYMMETRY study in patients with cirrhotic MASH (F4 fibrosis, compensated). Based on statistically significant fibrosis regression and MASH resolution among patients with biopsy-confirmed pre-cirrhotic MASH, as well as a trend toward fibrosis improvement and statistically significant MASH resolution among patients with cirrhosis due to MASH, the Company believes EFX has the potential, if approved, to be an important medicine for treating MASH.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, completion and success of clinical testing, development by competitors of new technological innovations, compliance with governmental regulations, dependence on key personnel and protection of proprietary technology and the ability to secure additional capital to fund operations. EFX will require extensive clinical testing prior to regulatory approval and commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Basis of presentation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company after elimination of all intercompany accounts and transactions. All adjustments necessary for the fair presentation of the Company’s consolidated financial statements for the periods presented have been reflected.

Liquidity

In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are certain conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued.

Since its inception, the Company has raised $1,040,200 in capital funds, including $105,800 in proceeds from its initial public offering (“IPO”) in June 2019, $818,900 in proceeds from the sales of common stock in equity offerings between 2020 and 2023, which includes a $25,000 equity investment from Pfizer, Inc. in 2022, $90,500 in proceeds from the sale of redeemable convertible preferred stock and $25,000 in venture debt borrowings. The Company has incurred recurring losses since its inception, including net losses of $151,759, $112,033 and $100,777 for the years ended December 31, 2023, 2022 and 2021, respectively. In addition, as of December 31, 2023, the Company had an accumulated deficit of $574,096. The Company expects to continue to generate operating losses for the foreseeable future. As of the issuance date of these consolidated financial statements, the Company expects that its existing cash, cash equivalents, short and long-term marketable securities of $569,293 as of December 31, 2023, will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of these consolidated financial statements. The Company expects that it will require additional funding to complete the clinical

development of EFX, commercialize EFX, if it receives regulatory approval, and pursue in-licenses or acquisitions of other product candidates.

If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Amgen license agreement (Details) - USD ($)	1 Months Ended		3 Months Ended	12 Months Ended
Amgen license agreement (Details) - USD ($)	Nov. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued value under agreement					$ 24,647,000
Research and development expense				$ 141,798,000	85,284,000	$ 81,759,000
Amgen Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Initial fair value of the anti-dilution right liability	$ 7,404,000
Payment for clinical trail			$ 2,500,000
Obligation for payment in connection with dosing of the first patient			7,500,000
Amgen Agreement \| Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate milestone payments upon the achievement of specified commercial milestones			75,000,000
Payment in connection with dosing of the first patient			$ 30,000,000
Amgen Agreement \| Research and development expense
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense				$ 7,500,000	$ 0	$ 0
Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront payment		$ 5,000,000
Amgen Agreement \| Series A Preferred Stock
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued under agreement	3,205,128
Amgen Agreement \| Series A Preferred Stock \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued under agreement		2,653,333
Share Issued value under agreement		$ 1,353,000
Ownership Interest [Member] \| Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Ownership interest of the outstanding shares (as a percent)		10.00%

Nature of the business and basis of presentation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Clinicaltrial	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Organization, consolidation and presentation of financial statements [Line Items]
Additional Paid in Capital	$ 1,040,200
Proceeds from the sale of redeemable convertible preferred stock	90,500
Proceeds from its initial public offering	105,800
Proceeds from the sales of common stock in equity offerings	818,900
Venture debt borrowings	25,000
Proceeds from equity investment from Pfizer, Inc.	25,000
Net loss	151,759	$ 112,033	$ 100,777
Accumulated deficit	(574,096)	$ (422,337)
Cash, cash equivalents and short-term marketable securities	$ 569,293
SYMMETRY Study \| NASH Patients with Compensated Cirrhosis
Organization, consolidation and presentation of financial statements [Line Items]
Number of planned clinical trials \| Clinicaltrial	3

Net loss per share - Anti-Diluted (Details) - shares	12 Months Ended
Net loss per share - Anti-Diluted (Details) - shares	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings per share, total	7,455,527	6,092,733	5,221,094
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings per share, total	6,899,977	5,780,004	5,221,094
Unvested Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings per share, total	371,952	129,131
Warrants to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings per share, total	45,898	36,718
Warrants Available for Future Grant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from the calculation of diluted earnings per share, total	137,700	146,880

Income taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income taxes

10. Income taxes

During the years ended December 31, 2023, 2022 and 2021, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each period due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States.

A summary of the Company’s current and deferred tax provision is as follows:


	Year Ended December 31,
	2023			2022			2021
Current income tax provision:
Federal	$	—		$	—		$	—
State		—			—			—
Total current income tax provision		—			—			—
Deferred income tax benefit:
Federal		40,292			27,269			23,352
State		28,079			14,568			7,274
Total deferred income tax benefit		68,371			41,837			30,626
Change in deferred tax asset valuation allowance		(68,371	)		(41,837	)		(30,626	)
Total provision for income taxes	$	—		$	—		$	—

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2023				2022				2021
Federal statutory income tax rate		21.0		%		21.0		%		21.0		%
State income taxes, net of federal benefit		18.5				13.0				7.2
Research and development tax credits		2.4				2.4				2.0
Other permanent differences		2.6				0.8				(0.1	)
Change in deferred tax asset valuation allowance		(44.5	)			(37.2	)			(30.1	)
Effect of Section 382 limitation		-				-				-
Effective income tax rate		-		%		-		%		-		%

Net deferred tax assets as of December 31, 2023 and 2022 consisted of the following:


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carry forwards	$	88,219		$	68,450
Research and development tax credit carry forwards		12,846			7,704
License fees		5,545			3,355
Stock based compensation		14,286			8,974
Capitalized research and experimentation costs		58,610			20,803
Accruals, reserves and other		242			191
		179,748			109,477
Valuation allowance		(177,061	)		(108,690	)
Net deferred tax assets	$	2,687			787

Deferred tax liabilities:
Prepaid expenses		(2,687	)		(787	)
Net deferred tax liabilities	$	(2,687	)		(787	)

As of December 31, 2023, the Company had U.S. federal and state net operating loss carryforwards of $284,344 and $413,182, respectively, which may be available to offset future taxable income and begin to expire in 2037. The federal net operating loss carryforwards include $281,900, which may be carried forward indefinitely. As of December 31, 2023, the Company also had U.S. federal and state research and development tax credit carryforwards of $14,379 and $2,355, respectively, which may be available to offset future tax liabilities and begin to expire in 2033. During the year ended December 31, 2023, gross deferred tax assets, before valuation allowance, increased by $68,371, due to the operating loss incurred by the Company during that period.

Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income or tax liabilities. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three‑year period. The annual limitation is determined by multiplying the value of the Company's stock at the time of such ownership change by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the NOL carryforwards before utilization. As of December 31, 2023, the Company determined that ownership changes occurred on March 24, 2017, June 7, 2018 and July 8, 2020. As a result of the ownership changes, approximately $2,118 and $3,632 of the NOLs will expire unutilized for federal and state

purposes, respectively. The ability of the Company to use its remaining NOL carryforwards may be further limited if the Company experiences a Code Section 382 ownership change as a result of future changes in its stock ownership.

The Company’s research and development credits are subject to Code Section 383 and are limited due to the ownership changes that the Company has experienced. As of December 31, 2023, the Company has derecognized approximately $87 and $43 of gross federal and state research and development credits, respectively. The Company has not derecognized any of the California research and development credit-related deferred tax assets because the credits do not expire.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets at each reporting period. In doing so, the Company has considered its history of cumulative net losses incurred and its lack of commercialization of any products or generation of any revenue from product sales and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been recorded against the net deferred tax assets as of December 31, 2023 and 2022. Management reevaluates the positive and negative evidence at each reporting period.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2023 and 2022 related primarily to the increase in net operating loss carryforwards and research and development tax credit carryforwards and were as follows:


	2023			2022
Valuation allowance as of January 1,	$	(108,690	)	$	(66,853	)
Decreases recorded as a benefit to income tax provision		(68,371	)		(41,837	)
Valuation allowance as of December 31,	$	(177,061	)	$	(108,690	)

As of December 31, 2023, the Company had gross unrecognized tax benefits of $3,394, none of which if recognized, would reduce the effective tax rate in a future period, due to the Company's full valuation allowance on U.S. net deferred tax assets. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2023, the Company had not accrued interest or penalties related to uncertain tax positions and no amounts had been recognized in the Company’s consolidated statements of operations and comprehensive loss. For the year ended December 31, 2023, the Company will file income tax returns in the U.S., California, Connecticut, Colorado, Florida, Illinois, Kentucky, Maryland, Massachusetts, New York, New Jersey, North Carolina, Pennsylvania and Virginia, as prescribed by the tax laws of the jurisdictions in which it operates. The Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company is open to future tax examination under statute from 2019 to the present.

A reconciliation of the beginning and ending unrecognized tax benefits for the years ended December 31, 2023, 2022 and 2021 is as follows


Balance at December 31, 2020	$	644
Increases related to prior year tax positions		66
Increases related to current year tax positions		603
Balance at December 31, 2021		1,313
Increases related to prior year tax positions		51
Increases related to current year tax positions		746
Balance at December 31, 2022		2,110
Increases related to prior year tax positions		223
Increases related to current year tax positions		1,061
Balance at December 31, 2023	$	3,394

Beginning in 2022, the Tax Cuts and Jobs Act of 2017 eliminates the option to deduct research and development expenditures in the period incurred and requires amortization over five years or fifteen years pursuant to IRC Section 174. The Company is projected to remain in a taxable loss position even after the capitalization of R&D expenditures, and thus the new requirement is not expected to have a material impact on the Company’s financial position, results of operations or cash flows in 2023.

On September 8, 2023, the IRS released an advance version of Notice 2023-63 (“Notice”) which provides interim guidance to clarify the capitalization and amortization of specified research and experimental (“SRE”) expenditures under IRC Section 174, as amended by TCJA in 2017. The Notice addresses issues related to short tax years and the definition of the midpoint of the taxable year, the types of costs that constitute SRE expenditures including allocation methods, software development, research performed under contract, dispositions of property, and the treatment of SRE expenditures for long-term contract rules under section 460. The Notice also announces that the Treasury Department and the IRS intend to issue proposed regulations providing rules consistent with the guidance in the Notice applicable for tax years ending after September 8, 2023, and until then taxpayers may rely on the interim guidance in the notice, provided the taxpayer applies all of the rules in a consistent manner. The Company does not anticipate the guidance in the Notice to have material impact on the tax provision and will continue to monitor the development of the proposed regulations.

Accordingly, the Company is estimating 2023 and 2022 capitalization of U.S R&D expenditures net of 2023 and 2022 amortization of approximately $65,437 and $57,658 (an addback to estimated 2023 and 2022 US taxable income), respectively. Additionally, the requirement to capitalize and amortize foreign R&D expenses over 15 years resulted in 2023 and 2022 capitalization of R&D expenditures (net of amortization) of $65,899 and $14,728, respectively.

On August 16, 2022, the IRA was signed into law. The IRA includes implementation of a new alternative minimum tax, an excise tax on stock buybacks, and significant tax incentives for energy and climate initiatives, among other provisions. The Company is evaluating the provisions included under the IRA and does not expect the provisions to have a material impact to the Company’s consolidated financial statements.

All tax returns will remain open for examination by the federal and state taxing authorities for three and four years, respectively, from the date of utilization of any net operating loss carryforwards or research and development credits.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Schedule of maturity of the Company's operating lease liabilities

As of December 31, 2023, maturities of the Company’s operating lease liability was as follows:


2024	$	331
2025		341
2026		351
2027		208
Total future minimum lease payments		1,231
Less imputed interest		(152	)
Present value of operating lease liabilities	$	1,079

Schedule of components of operating lease expense

For the years ended December 31, 2023, 2022 and 2021, the components of operating lease cost were as follows:


		Year Ended December 31,
			2023				2022				2021
Lease cost:	Statement of Operations Classification:
Operating lease cost	General and administrative expense	$		324		$		324		$		324
Short-term lease cost	General and administrative expense			161				58				—
Variable operating lease cost	General and administrative expense			37				58				17
Total operating lease cost		$		522		$		440		$		341

Other information:
Cash paid for amounts included in the measurement of operating lease liability		$		321		$		312		$		303
Weighted average remaining lease term (years)				3.6				4.6				5.6
Weighted average discount rate				7.6	%			7.6	%			7.6	%