0001628280-24-006144 | 10-K | XBRL Viewer

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Income taxes - Schedule of effective income tax rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income tax benefit computed at federal statutory tax rate	21.00%	21.00%
State tax—net of federal	4.20%	8.00%
Federal credits	3.50%	1.40%
State credits	1.40%	0.10%
Other permanent differences	(0.20%)	(0.80%)
Withholding tax	(0.90%)	0.00%
Stock-based compensation	(2.80%)	(3.00%)
Valuation allowance	(27.20%)	(26.70%)
Total	(1.00%)	0.00%

Property and equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Summary of property and equipment

Depreciation on equipment is calculated using the straight-line method over the estimated useful lives of the assets as follows:


Asset category						Estimated useful life
Laboratory equipment						5 years
Computer equipment						3 years
Office equipment, furniture and fixtures						5 years
Leasehold improvements						Lesser of useful life or remaining lease term

Property and equipment consisted of the following (in thousands):


	As of December 31,
	2023		2022
Property and equipment
Laboratory equipment	$	8,042	$	8,757
Leasehold improvements	4,712		4,682
Furniture and fixtures	1,422		1,181
Office equipment	621		529
Computer equipment	98		191
Construction in progress	—		183
Total property and equipment	14,895		15,523
Less: accumulated depreciation	(7,763)		(8,123)
Total property and equipment, net	$	7,132	$	7,400

Summary of depreciation expense

Depreciation expense related to property and equipment was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Depreciation expense	$	1,578	$	1,676

Marketable securities

12 Months Ended

Dec. 31, 2023

Marketable Securities [Abstract]

Marketable securities

Marketable securities at December 31, 2023 consisted of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable securities, current:
Corporate debt securities	$	100,903	$	16	$	(221)	$	100,698
U.S. government debt securities	20,457		14		(43)		20,428
U.S. Treasury securities	5,965		1		—		5,966
Marketable securities, non-current
Corporate debt securities	27,901		120		(14)		28,007


Total marketable securities, current and non-current	$	155,226	$	151	$	(278)	$	155,099

Marketable securities at December 31, 2022 consisted of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable securities, current:
Corporate debt securities	$	183,270	$	2	$	(2,068)	$	181,204
U.S. government debt securities	40,986		—		(1,184)		39,802
U.S. Treasury securities	25,650		—		(257)		25,393
Marketable securities, non-current
Corporate debt securities	53,592		2		(471)		53,123
U.S. government debt securities	8,000		—		(161)		7,839

Total marketable securities, current and non-current	$	311,498	$	4	$	(4,141)	$	307,361

Marketable securities classified as current have maturities of less than one year. Marketable securities classified as non-current are those that: (i) have a maturity of greater than one year, and (ii) we do not intend to liquidate within the next twelve months, although these funds are available for use and, therefore, are classified as available-for-sale. No available-

for-sale debt securities held as of December 31, 2023 or December 31, 2021 had remaining maturities greater than five years.

Marketable securities in unrealized loss positions as of December 31, 2023 consisted of the following (in thousands, except number of securities):


	Number of Securities	Fair Value		Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months:
Corporate debt securities	64	$	68,563	$	(146)
U.S. government debt securities	9	11,914		(22)

Marketable securities in continuous unrealized loss position for greater than 12 months:
Corporate debt securities	18	22,138		(89)
U.S. government debt securities	3	5,979		(21)

Total marketable securities in unrealized loss position	94	$	108,594	$	(278)

Marketable securities in unrealized loss positions as of December 31, 2022 consisted of the following (in thousands, except number of securities):


	Number of Securities	Fair Value		Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months:
Corporate debt securities	63	$	134,027	$	(1,262)
U.S. government debt securities	6	15,748		(245)
U.S. Treasury securities	4	5,575		(11)
Marketable securities in continuous unrealized loss position for greater than 12 months:
Corporate debt securities	36	82,375		(1,277)
U.S. government debt securities	7	31,892		(1,100)
U.S. Treasury securities	4	19,817		(246)
Total marketable securities in unrealized loss position	120	$	289,434	$	(4,141)

Based on factors such as historical experience, market data, issuer-specific factors, and current economic conditions, the Company did not record an allowance for credit losses at December 31, 2023 and December 31, 2022, related to these securities.

Stock-based compensation - Summary of stock option activity (Details) - 2020 Stock Option and Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Options outstanding, beginning balance (in shares)	6,993,052
Options granted (in shares)	4,180,270
Options exercised (in shares)	(13,096)
Options forfeited/expired (in shares)	(1,685,217)
Options outstanding, ending balance (in shares)	9,475,009	6,993,052
Options exercisable (in shares)	3,838,707
Options vested and expected to vest (in shares)	9,475,009
Weighted-Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 21.57
Options granted (in dollars per share)	3.87
Options exercised (in dollars per share)	4.46
Options forfeited/expired (in dollars per share)	18.48
Options outstanding, ending balance (in dollars per share)	14.34	$ 21.57
Options exercisable (in dollars per share)	20.54
Options vested and expected to vest (in dollars per share)	$ 14.34
Options, Additional Disclosures
Weighted average remaining contractual term, outstanding	7 years 7 months 9 days	7 years 9 months 10 days
Weighted average remaining contractual term, exercisable	6 years 8 months 4 days
Weighted average remaining contractual term, vested and expected to vest	7 years 7 months 9 days
Aggregate intrinsic value, outstanding	$ 8,261	$ 1,031
Aggregate intrinsic value, exercisable	482
Aggregate intrinsic value, vested and expected to vest	$ 8,261

Cover - USD ($)	12 Months Ended
Cover - USD ($)	Dec. 31, 2023	Feb. 14, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Document Transition Report	false
Entity File Number	001-39567
Entity Registrant Name	C4 Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-5617627
Entity Address, Address Line One	490 Arsenal Way
Entity Address, Address Line Two	Suite 120
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Local Phone Number	231-0700
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	CCCC
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 129,573,953
Entity Common Stock, Shares Outstanding		68,600,669
Amendment Flag	false
Entity Central Index Key	0001662579
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement for its 2023 Annual Meeting of Stockholders to be filed pursuant to Regulation 14A within 120 days of the end of the registrant’s fiscal year ended December 31, 2023 are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.

Marketable securities - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Marketable Securities [Abstract]
Allowance for credit loss	$ 0	$ 0

Stock-based compensation - Schedule of stock-based compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 27,235	$ 30,016
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	11,826	13,108
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 15,409	$ 16,908

Income taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating losses	$ 61,036	$ 54,300
Capitalized research and experimental expenditures	51,401	27,568
Operating lease liability	20,611	21,443
R&D and investment tax credits	18,049	11,519
Stock-based compensation	9,061	6,296
Deferred revenue	3,881	8,457
Foreign tax credit	1,204	0
Capitalized start-up costs	555	699
Unrealized gain/loss	0	1,090
Other	27	354
Total gross deferred tax assets	165,825	131,726
Deferred tax liabilities:
Right-of-use asset	(18,573)	(19,868)
Fixed assets	(1,663)	(1,738)
Less: valuation allowance	(145,589)	(110,120)
Net deferred taxes	$ 0	$ 0

Marketable securities - Summary of marketable securities in unrealized loss position (Details) $ in Thousands	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Number of Securities
Total marketable securities in unrealized loss position, Number of securities \| security	94	120
Fair Value
Total marketable securities in unrealized loss position	$ 108,594	$ 289,434
Gross Unrealized Losses
Total marketable securities in unrealized loss position	$ (278)	$ (4,141)
Corporate debt securities
Number of Securities
Marketable securities in continuous unrealized loss position for less than 12 months, Number of securities \| security	64	63
Marketable securities in continuous unrealized loss position for greater than 12 months, Number of securities \| security	18	36
Fair Value
Marketable securities in continuous unrealized loss position for less than 12 months	$ 68,563	$ 134,027
Marketable securities in continuous unrealized loss position for greater than 12 months	22,138	82,375
Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months	(146)	(1,262)
Marketable securities in continuous unrealized loss position for greater than 12 months	$ (89)	$ (1,277)
U.S. government debt securities
Number of Securities
Marketable securities in continuous unrealized loss position for less than 12 months, Number of securities \| security	9	6
Marketable securities in continuous unrealized loss position for greater than 12 months, Number of securities \| security	3	7
Fair Value
Marketable securities in continuous unrealized loss position for less than 12 months	$ 11,914	$ 15,748
Marketable securities in continuous unrealized loss position for greater than 12 months	5,979	31,892
Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months	(22)	(245)
Marketable securities in continuous unrealized loss position for greater than 12 months	$ (21)	$ (1,100)
U.S. Treasury securities
Number of Securities
Marketable securities in continuous unrealized loss position for less than 12 months, Number of securities \| security		4
Marketable securities in continuous unrealized loss position for greater than 12 months, Number of securities \| security		4
Fair Value
Marketable securities in continuous unrealized loss position for less than 12 months		$ 5,575
Marketable securities in continuous unrealized loss position for greater than 12 months		19,817
Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months		(11)
Marketable securities in continuous unrealized loss position for greater than 12 months		$ (246)

Net loss per share - Schedule of antidilutive securities excluded from computation of earnings per share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	9,475,009	6,993,052

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

In July 2017, the Company entered into a lease of office and laboratory space for its headquarters in Watertown, Massachusetts, or the Watertown Lease. The Watertown Lease had a non-cancelable term of ten years with an option to extend for one additional five-year period and is subject to rent escalation throughout the term. Additionally, the Watertown Lease required the Company to provide collateral, which was recorded as restricted cash on the consolidated balance sheets. The Watertown Lease commenced in April 2018. The Watertown Lease was classified as an operating lease and, upon the commencement in April 2018, the Company recorded a lease liability of $15.1 million and a right-of-use asset of $16.7 million, which is inclusive of $1.5 million of construction costs funded by the Company. In initially calculating the lease liability and the right-of-use asset, the Company did not include the additional five-year period option as management did not believe there was reasonable certainty that the Company would exercise the option. In addition to rent, the Company is also responsible for paying its pro rata share of costs incurred for common area maintenance, real estate taxes and property insurance related to the leased space, which are accounted for as variable lease costs.

In November 2021, the Company entered into an amendment to the Watertown Lease, or the Amended Lease. The Amended Lease serves to extend the lease term of the Company’s existing leased space, or the Existing Leased Space, and provides additional office and laboratory space, or the Newly Leased Space. The Amended Lease commenced in January 2022 and the Company’s obligation to pay rent on the Newly Leased Space commenced in March 2022, with the amount of this new rent obligation added to the Company’s continuing obligation to pay rent on the Existing Leased Space. The Amended Lease terminates in March 2032, which is 10 years from the rent commencement date for the Newly Leased Space. The Amended Lease is subject to fixed rate rent escalations, provides for up to $2.6 million in tenant improvements, and provides an option for the Company to extend the lease term of the Amended Lease for one additional five-year period. Upon executing the Amended Lease, the Company increased its collateral to $3.3 million, which is recorded as restricted cash on the accompanying consolidated balance sheets as of December 31, 2023 and 2022. In addition to rent, under the terms of the Amended Lease, the Company is also responsible for paying its pro rata share of costs incurred for common area maintenance, real estate taxes and property insurance related to the leased space, including both the Existing Leased Space and, as of January 2022, the Newly Leased Space, which amounts are accounted for as variable lease costs.

Accounting for the amended lease

As the Amended Lease extends the term of the Existing Leased Space and provides access to the Newly Leased Space, in accordance with the provisions of ASC 842, the Company accounted for the Amended Lease as two separate contracts: 1) modification of the existing lease agreement to extend the lease term of the Existing Leased Space, and 2) new lease agreement for the right-of-use of the Newly Leased Space.

As the Company maintained control of the Existing Leased Space upon execution of the Amended Lease, the Company recorded an increase in right-of-use asset and lease liability of $20.1 million related to the new rental payments during the extended term and current incremental borrowing rate of the Existing Leased Space upon execution of the Amended Lease. The calculation of the lease liability and the right-of-use asset of the Existing Leased Space does not include the additional five-year period option as the Company does not believe there is reasonable certainty that the option will be exercised.

As noted above, the lease for the Newly Leased Space commenced in January 2022. As a result, the Company recorded a right-of-use asset of $44.4 million, and a corresponding lease liability of $44.1 million for the Newly Leased Space. The calculation of the lease liability and the right-of-use asset of the Newly Leased Space does not include the additional five-year period option provided under the Amended Lease as the Company does not believe there is reasonable certainty that the option will be exercised. As stated above, the Amended Lease provides for up to $2.6 million of tenant improvement allowance which was used in full in the year ended December 31, 2022.

In May 2022, the Company entered into a sublease agreement with a third party, or the Sublease, for a portion of the office and laboratory space in Suite 200 at 490 Arsenal Way, Watertown, Massachusetts. The term of the Sublease ends in June 2025.

The elements of lease costs were as follows (in thousands):


	Years Ended December 31,
	2023		2022
Lease cost:
Operating lease cost	$	10,030	$	10,031
Variable lease cost	1,979		2,026
Sublease income	(2,577)		(1,481)
Total lease cost	$	9,432	$	10,576

The following table summarizes the lease term and incremental borrowing rate applied in arriving at the lease liability:


	As of December 31,
	2023		2022
Remaining lease term	8.1 years		9.1 years
Incremental borrowing rate	5.3	%	5.3	%

Future lease payments under non-cancelable leases as of December 31, 2023 for each of the years ending December 31 are as follows (in thousands):


Undiscounted lease payments:
2024	$	8,828
2025	9,093
2026	9,366
2027	9,646
2028	11,362
Thereafter	40,751
Total undiscounted lease payments	89,046
Less: imputed interest	(18,070)
Total operating lease liability as of December 31, 2023	$	70,976

Long-term debt and warrant – related party

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Long-term debt and warrant – related party

Long-term debt – related party consisted of the following (in thousands):


	December 31, 2022
Term Loan — related party, net of unamortized debt issuance costs and debt discount of $1,018 at December 31, 2022	$	11,482
Less: current portion	2,287
Total long-term debt — related party, net of current and discount	9,195

On June 5, 2020, contemporaneously with the completion of its Series B Financing, the Company entered into a Credit Agreement, or the Credit Agreement, with Perceptive Credit Holdings III, LP, an affiliate of Perceptive Advisors LLC, or Perceptive, that provided for an aggregate principal borrowing amount of up to $20.0 million, available in two tranches of $12.5 million and $7.5 million. Perceptive was considered a related party to the Company based on its ownership of the Company’s common stock at inception of the Credit Agreement.

In June 2020, the Company drew down on the first tranche of $12.5 million, or the Term Loan. The Company elected not to draw down the second tranche, which expired on June 30, 2021.

On May 17, 2023, the Company entered into an amendment to the Credit Agreement pursuant to which the Company and its lender agreed to replace the LIBOR benchmark with SOFR, which is regulated by the Federal Reserve Bank of New York. The Company amended its Credit Agreement due to the Financial Conduct Authority's planned phase-out of LIBOR on June 30, 2023. The use of the SOFR rate became effective as of July 1, 2023.

In July 2023, the Company's obligation to pay a prepayment fee was extinguished based on the terms of the Credit Agreement. On July 26, 2023, the Company elected to repay the remaining outstanding principal balance on the Term Loan. In connection with the repayment of the outstanding balance on the Term Loan, the liens on substantially all of the Company's assets were released. The Company incurred a $0.6 million loss on the extinguishment of this debt for the year ended December 31, 2023.

Interest expense for the years ended December 31, 2023 and 2022, was $1.0 million and $1.5 million.

Fair value measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair value measurements

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values as of December 31, 2023 (in thousands):


	Fair Value		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	103,564	$	103,564	$	—	$	—
U.S. Treasury securities	14,972		—		14,972		—
Corporate debt securities	7,588		—		7,588		—
Marketable securities:
Corporate debt securities	128,705		—		128,705		—
U.S. government debt securities	20,428		—		20,428		—
U.S. Treasury securities	5,966		—		5,966		—
Total cash equivalents and marketable securities	$	281,223	$	103,564	$	177,659	$	—

The following table sets forth the fair value of the Company’s financial assets by level within the fair value hierarchy at December 31, 2022 (in thousands):


	Fair Value		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	28,705	$	28,705	$	—	$	—

U.S. Treasury securities	799		—		799		—
Marketable securities:
Corporate debt securities	234,327		—		234,327		—
U.S. government debt securities	47,641		—		47,641		—
U.S. Treasury securities	25,393		—		25,393		—
Total cash equivalents and marketable securities	$	336,865	$	28,705	$	308,160	$	—

The Company classifies its money market funds, which are valued based on quoted market prices in active markets, with no valuation adjustment, as Level 1 assets within the fair value hierarchy.

Marketable securities consist of U.S. Treasury securities, U.S. government debt securities, and corporate debt securities, all of which are classified as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities. Marketable securities are classified within Level 2 of the fair value hierarchy because pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date, and fair value is determined using models or other valuation methodologies on a recurring basis.

- 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

Subsequent events	12 Months Ended
Subsequent events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent events	Subsequent event On January 9, 2024, the Company implemented a plan to reduce operating costs and better align its workforce with the needs of its business. Under the cost reduction plan, the Company reduced its workforce by approximately 30%. The Company estimates that it will incur one-time restructuring charges of approximately $2.7 million including employee severance, benefits and related termination costs, the majority of which the Company expects to pay in the first quarter of 2024.

Long-term debt and warrant – related party - Schedule of long-term debt (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Term Loan — related party, net of unamortized debt issuance costs and debt discount of $1,018 at December 31, 2022		$ 11,482
Long-term debt, net of debt discount—related party, current	$ 0	2,287
Long-term debt, net of debt discount—related party, net of current	$ 0	9,195
Unamortized debt issuance costs and debt discount		$ 1,018

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Fair value measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 155,099	$ 307,361
Total cash equivalents and marketable securities	281,223	336,865
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	128,705	234,327
U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	20,428	47,641
U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	5,966	25,393
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	103,564	28,705
U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	14,972	799
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	7,588
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	103,564	28,705
Level 1 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 1 \| U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 1 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 1 \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	103,564	28,705
Level 1 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 1 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	177,659	308,160
Level 2 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	128,705	234,327
Level 2 \| U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	20,428	47,641
Level 2 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	5,966	25,393
Level 2 \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 2 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	14,972	799
Level 2 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	7,588
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 3 \| U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 3 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0	0
Level 3 \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	$ 0
Level 3 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 0

Income taxes - Summary of income tax (benefit) expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Current tax provision:
Current federal provision	$ 0	$ 0
Current state provision	76	0
Current foreign provision	1,204	0
Total current provision	1,280	0
Deferred tax provision:
Deferred federal provision	0	0
Deferred state provision	0	0
Deferred foreign provision	0	0
Total tax provision	$ 1,280	$ 0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Revenue from collaboration agreements	$ 20,756	$ 31,096
Operating expenses:
Research and development	117,706	117,841
General and administrative	42,081	42,789
Total operating expenses	159,787	160,630
Loss from operations	(139,031)	(129,534)
Other income (expense), net
Interest expense and amortization of long-term debt—related party	(1,373)	(2,216)
Loss on early extinguishment of debt	(621)	0
Interest and other income, net	9,812	3,575
Total other income (expense), net	7,818	1,359
Loss before income taxes	(131,213)	(128,175)
Income tax expense	(1,280)	0
Net loss	$ (132,493)	$ (128,175)
Net loss per share — basic (in dollars per share)	$ (2.67)	$ (2.62)
Net loss per share — diluted (in dollars per share)	$ (2.67)	$ (2.62)
Weighted-average number of shares - basic (in shares)	49,640,505	48,861,665
Weighted-average number of shares - diluted (in shares)	49,640,505	48,861,665
Other Comprehensive gain (loss):
Unrealized gain (loss) on marketable securities	$ 4,010	$ (3,362)
Comprehensive loss	$ (128,483)	$ (131,537)
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]	Collaborative Arrangement [Member]	Collaborative Arrangement [Member]

Long-term debt and warrant – related party (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Long-Term Debt Instruments

Long-term debt – related party consisted of the following (in thousands):


	December 31, 2022
Term Loan — related party, net of unamortized debt issuance costs and debt discount of $1,018 at December 31, 2022	$	11,482
Less: current portion	2,287
Total long-term debt — related party, net of current and discount	9,195

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
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-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

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+ Details

Marketable securities - Summary of marketable securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Marketable securities, current:
Fair Value	$ 127,091	$ 246,399
Marketable securities, non-current
Fair Value	28,008	60,962
Amortized Cost	155,226	311,498
Gross Unrealized Gains	151	4
Gross Unrealized Losses	(278)	(4,141)
Fair Value	155,099	307,361
Corporate debt securities
Marketable securities, current:
Amortized Cost	100,903	183,270
Gross Unrealized Gains	16	2
Gross Unrealized Losses	(221)	(2,068)
Fair Value	100,698	181,204
Marketable securities, non-current
Amortized Cost	27,901	53,592
Gross Unrealized Gains	120	2
Gross Unrealized Losses	(14)	(471)
Fair Value	28,007	53,123
Fair Value	128,705	234,327
U.S. government debt securities
Marketable securities, current:
Amortized Cost	20,457	40,986
Gross Unrealized Gains	14	0
Gross Unrealized Losses	(43)	(1,184)
Fair Value	20,428	39,802
Marketable securities, non-current
Amortized Cost		8,000
Gross Unrealized Gains		0
Gross Unrealized Losses		(161)
Fair Value		7,839
Fair Value	20,428	47,641
U.S. Treasury securities
Marketable securities, current:
Amortized Cost	5,965	25,650
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(257)
Fair Value	5,966	25,393
Marketable securities, non-current
Fair Value	$ 5,966	$ 25,393

Leases - Summary of future lease payments (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Leases [Abstract]
2024	$ 8,828
2025	9,093
2026	9,366
2027	9,646
2028	11,362
Thereafter	40,751
Total undiscounted lease payments	89,046
Less: imputed interest	(18,070)
Total operating lease liability as of December 31, 2023	$ 70,976

Nature of the business	12 Months Ended
Nature of the business	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the business	Nature of the business C4 Therapeutics, Inc., or, together with its subsidiary, the Company, is a clinical-stage biopharmaceutical company dedicated to delivering on the promise of Targeted Protein Degradation, or TPD, science to create a new generation of small-molecule medicines that transform patients’ lives. By leveraging its proprietary TORPEDO platform, the Company has the capability to efficiently design and optimize small molecule protein degraders that are highly active against their desired targets by harnessing the body’s natural process for destroying unwanted proteins. The Company believes its novel oral product candidates have the potential to overcome drug resistance often seen with inhibitors, target currently “undruggable” targets and improve patient outcomes. The Company was incorporated in Delaware on October 7, 2015 and has its principal office in Watertown, Massachusetts. Liquidity and capital resources Since its inception, the Company’s primary activities have been focused on performing research and development activities, building the Company’s intellectual property, recruiting personnel, and raising capital to support these activities. To date, the Company has funded its operations primarily with proceeds received from the sales of redeemable convertible preferred stock, public offerings of the Company’s common stock, through its collaboration agreements, and debt financing. The Company has incurred recurring losses since its inception, including net losses of $132.5 million and $128.2 million for the years ended December 31, 2023 and 2022, respectively. In addition, as of December 31, 2023, the Company had an accumulated deficit of $528.4 million. To date, the Company has not generated any revenue from product sales as none of its product candidates has been approved for commercialization. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents, and marketable securities of $281.7 million as of December 31, 2023 will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these consolidated financial statements. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Risks and uncertainties The Company is subject to risks common to other life science companies in the early development stage including, but not limited to, uncertainty of ability to raise additional financing, product development and commercialization, development by its competitors of new technological innovations, dependence on key personnel, market acceptance of products, lack of marketing and sales history, product liability, protection of proprietary technology and intellectual property, and compliance with the Food and Drug Administration, or the FDA, and other government regulations. If the Company does not successfully advance its programs into and through human clinical trials and commercialize any of its product candidates either directly or through collaborations with other companies, the Company may be unable to produce product revenue or achieve profitability. There can be no assurance that the Company’s research and development efforts will be successful, adequate protection for the Company’s intellectual property will be obtained, any products developed will obtain necessary government regulatory approval, or any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies.

Collaboration and license agreements - Schedule of supplemental financial information related to collaboration and license agreements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue recognized that was included in the contract liability at the beginning of the period	$ 20,185	$ 25,412
Revenue recognized from performance obligations fully or partially satisfied in previous periods	$ 43	$ 518

Stock-based compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

2015 Incentive Stock Option and Grant Plan

On December 28, 2015, the Company’s board of directors adopted the 2015 Incentive Stock Option and Grant Plan, or the 2015 Plan, and reserved 2,525,327 shares of common stock for issuance under this plan.

The 2015 Plan authorized the board of directors or a committee of the board to grant incentive stock options, nonqualified stock options and restricted stock awards to eligible employees, outside directors and consultants of the Company. Options granted under the 2015 Plan generally vest over a period of five or eight years with a cliff vesting at one year and quarterly vesting thereafter and options that lapse or are forfeited are available to be granted again. The contractual life of all options granted under the 2015 Plan is ten years from the date of grant.

2020 Stock Option and Incentive Plan

On September 8, 2020, the Company’s board of directors adopted the C4 Therapeutics, Inc. 2020 Stock Option and Incentive Plan, or the 2020 Plan, which became effective on September 30, 2020. Upon adoption there were 6,567,144 shares of common stock reserved for issuance under the 2020 Plan. The Company’s Board of Directors, the Compensation Committee of the Board of Directors, and, in certain contexts, the Chief Executive Officer of the Company are authorized to grant a broad range of stock-based awards under the 2020 Plan, including stock options, stock appreciation rights, or SARs, restricted stock awards, or RSAs, restricted stock units, or RSUs, performance awards and stock bonus awards to the Company’s officers, employees, directors and other key persons, including consultants.

Following the effectiveness of the 2020 Plan, the Company ceased making grants under the 2015 Plan. However, the 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. Shares of common stock subject to awards granted under the 2015 Plan that cease to be subject to such awards by forfeiture or otherwise after the termination of the 2015 Plan will be available for issuance under the 2020 Plan. As of December 31, 2023, there were 3,358,336 shares available for future grant under the 2020 Plan.

The 2020 Plan provides for an annual increase, to be added on the first day of each fiscal year, beginning with January 1, 2021 and continuing until the expiration of the 2020 Plan, equal to the lesser of (i) 5% of the outstanding shares of common stock on the immediately preceding December 31st, or (ii) lesser number of shares determined by the administrator of the 2020 Plan, which is the Company’s Board of Directors or the Compensation Committee of the Board of Directors. On January 1, 2024, the annual increase for the 2020 Plan resulted in an additional 3,023,359 shares authorized for issuance being added to the 2020 Plan.

Stock-based compensation expense was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Stock-based compensation expense:
Research and development	$	11,826	$	13,108
General and administrative	15,409		16,908
Total stock-based compensation expense	$	27,235	$	30,016

The following table summarizes the stock option activity under the Company’s equity awards plans for the year ended December 31, 2023:


	Number of Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	6,993,052	$	21.57	7.78	$	1,031
Granted	4,180,270	3.87
Exercised	(13,096)	4.46
Forfeited/expired	(1,685,217)	18.48
Outstanding as of December 31, 2023	9,475,009	$	14.34	7.61	$	8,261
Exercisable as of December 31, 2023	3,838,707	$	20.54	6.68	$	482
Vested and expected to vest as of December 31, 2023	9,475,009	$	14.34	7.61	$	8,261

Other information related to the option activity of the Company was as follows:


	Years Ended December 31,
	2023		2022
Weighted-average fair value of options granted	$	2.84	$	13.44
Intrinsic value of options exercised (in thousands)	$	22	$	1,796

As of December 31, 2023, the unrecognized compensation cost related to outstanding options was $51.6 million, which is expected to be recognized over a weighted-average period of 2.1 years.

The following table summarizes assumptions used in the Black-Scholes option pricing model to determine the fair value of stock options granted to employees:


	Years Ended December 31,
	2023	2022
Expected option life (years)	5.50 - 6.11	5.50 - 6.11
Risk-free interest rate	3.45% - 4.73%	1.47% - 4.22%
Expected volatility	81.99% - 86.15%	81.36% - 88.75%
Expected dividend yield	0.00%	0.00%

Performance-based restricted stock units

In January and February 2022, the Company’s Board of Directors authorized an issuance of 563,500 performance-based restricted stock units, or PSUs, to certain employees, including members of the Company’s leadership team under the 2020 Plan. Vesting of the PSUs are contingent upon the determination of achievement of certain discovery and clinical milestones, or as specified market conditions are met. Upon vesting, each PSU converts automatically into one share of the Company’s common stock.

The following table summarizes the activity under the Company’s equity plans with respect to PSUs for the year ended December 31, 2023:


	Shares	Weighted-Average Grant Date Fair Value
Outstanding as of December 31, 2022	465,291	$	25.09
Granted	—	—
Vested (1)	(135,301)	26.52
Forfeited	(175,990)	28.91
Outstanding as of December 31, 2023	154,000	$	19.47

(1) Vested PSUs include 17,556 shares retained by the Company to cover statutory minimum withholding taxes.

As of December 31, 2023, the unrecognized compensation cost related to outstanding PSUs was $3.1 million which is expected to be recognized over a weighted-average period of 1.2 years.

Time-based restricted stock units

In January and February 2023, the Company’s Board of Directors authorized an issuance of 824,600 time-based restricted stock units, or RSUs, to employees under the 2020 Plan. Vesting of the RSUs are contingent to time-based vesting conditions. These RSUs are valued on the grant date using the grant date market price of the underlying shares. Upon vesting, each RSU automatically converts into one share of the Company’s common stock.

The following table summarizes the activity under the Company’s equity plans with respect to RSUs for the year ended December 31, 2023:


	Shares	Weighted-Average Grant Date Fair Value
Outstanding as of December 31, 2022	—	$	—
Granted	824,600	5.37
Vested	—	—
Forfeited	(74,390)	5.67
Outstanding as of December 31, 2023	750,210	$	5.35

As of December 31, 2023, the unrecognized compensation cost related to outstanding RSUs was $3.5 million which is expected to be recognized over a weighted-average period of 3.2 years.

Inducement grants

On two separate dates in July 2023, the Company's Board of Directors approved the grant of non-qualified stock options to purchase an aggregate of 351,000 shares of the Company's common stock to two new employees. Options granted under these inducement grants vest over a period of four years with a cliff vesting at one year and quarterly vesting thereafter. As of December 31, 2023, none of these stock options have vested or been forfeited, and 351,000 options remain outstanding under these inducement awards.

2020 Employee Stock Purchase Plan

In September 2020, the Company’s Board of Directors adopted the C4 Therapeutics, Inc. 2020 Employee Stock Purchase Plan, or the 2020 ESPP. Eligible employees may authorize payroll deductions of up to 15% of their eligible compensation during an offering period. The Company may hold one or more offering periods each year during which employees will be able to purchase shares under the 2020 ESPP. The Company issued 133,784 shares during the year ended December 31, 2023.

As of December 31, 2023, the Company had 1,673,129 shares available for future issuance under the 2020 ESPP. The 2020 ESPP provides for an annual increase to be added on the first day of each fiscal year, beginning with January 1, 2021 and continuing thereafter through January 1, 2030, equal to the lesser of (i) 1% of the outstanding shares of common stock on the immediately preceding December 31st, (ii) 656,714 shares, or (ii) lesser number of shares determined by the administrator of the 2020 ESPP. On January 1, 2024, the annual increase for the 2020 ESPP resulted in an additional 604,671 shares authorized for issuance being added to the 2020 ESPP.

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
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	60,467,188	48,966,216
Common stock, shares outstanding	60,467,188	48,966,216

Net loss per share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Schedule of antidilutive securities excluded from computation of earnings per share

The Company excluded the following potential common shares presented based on amounts outstanding at 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
Options to purchase common stock	9,475,009	6,993,052

Schedule of basic and diluted loss per share

Basic and diluted loss per share is computed by dividing net loss by the weighted-average common shares outstanding (in thousands, except share and per share data):


	Years Ended December 31,
	2023		2022
Numerator:


Net loss —basic and diluted	$	(132,493)	$	(128,175)
Denominator:
Weighted-average common stock outstanding—basic and diluted	49,640,505		48,861,665
Net loss per share —basic and diluted	$	(2.67)	$	(2.62)

Accrued expenses and other current liabilities

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	As of December 31,
	2023		2022
Accrued expenses and other current liabilities:
Accrued research and development	$	11,243	$	9,824
Accrued compensation and benefits	7,344		6,831

Other	2,043		3,114
Total accrued expenses and other current liabilities	$	20,630	$	19,769

As of December 31, 2023 there were $3.1 million of costs related to wind down activities for CFT8634 included within the accrued research and development balance.

Stockholders equity	12 Months Ended
Stockholders equity	Dec. 31, 2023
Equity [Abstract]
Stockholder's equity	Stockholders’ equity Common stock In October 2020, the Company authorized preferred stock issuable of 10,000,000 shares and increased its authorized common stock issuable to 150,000,000 shares, both with a $0.0001 par value per share. The holders of common stock are entitled to one vote for each share held at all meetings of stockholders and written actions in lieu of meetings provided. Subject to full payment of all preferential dividends to which the holders of preferred stock, if any, are entitled, the holders of common stock shall be entitled to receive dividends out of funds legally available. In the event of a liquidation, dissolution, or winding up of the Company, after payment or provision for payment of all debts and liabilities of the Company and all preferential amounts to which the holders of preferred stock, if any, are entitled with respect to the distribution of assets in liquidation, the holders of common stock shall be entitled to share ratably in the remaining assets of the Company available for distribution. The holders of common stock have no preemptive or other subscription rights, and there are no redemption or sinking fund provisions with respect to such stock. At-The-Market Equity Program In November 2021, the Company filed an automatically effective registration statement on Form S-3, or the Registration Statement, with the SEC that registers the offering, issuance and sale of an unspecified amount of common stock, preferred stock, debt securities, warrants and/or units of any combination thereof. Simultaneously, the Company entered into an equity distribution agreement with Cowen and Company, LLC, as sales agent, to provide for the issuance and sale by the Company of up to $200.0 million of common stock from time to time in “at-the-market” offerings under the Registration Statement and related prospectus filed with the Registration Statement, or the ATM Program. For the year ended December 31, 2023, 11,186,142 shares for net proceeds of $57.7 million, were settled under the ATM Program. In January 2024, 2,500,601 shares were settled for net proceeds of $14.1 million. Based on the December 2023 and January 2024 activity described above, the Company has sold a total of 13,686,743 shares of its common stock at a average price of $5.42 per share for proceeds, net of commissions and fees, of $71.8 million. No sales were made under the ATM program for the year ended December 31, 2022.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

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

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

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Accrued expenses and other current liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Summary of accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	As of December 31,
	2023		2022
Accrued expenses and other current liabilities:
Accrued research and development	$	11,243	$	9,824
Accrued compensation and benefits	7,344		6,831

Other	2,043		3,114
Total accrued expenses and other current liabilities	$	20,630	$	19,769

Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of property and equipment

Depreciation on equipment is calculated using the straight-line method over the estimated useful lives of the assets as follows:


Asset category						Estimated useful life
Laboratory equipment						5 years
Computer equipment						3 years
Office equipment, furniture and fixtures						5 years
Leasehold improvements						Lesser of useful life or remaining lease term

Property and equipment consisted of the following (in thousands):


	As of December 31,
	2023		2022
Property and equipment
Laboratory equipment	$	8,042	$	8,757
Leasehold improvements	4,712		4,682
Furniture and fixtures	1,422		1,181
Office equipment	621		529
Computer equipment	98		191
Construction in progress	—		183
Total property and equipment	14,895		15,523
Less: accumulated depreciation	(7,763)		(8,123)
Total property and equipment, net	$	7,132	$	7,400

Collaboration and license agreements - Schedule of revenue from collaboration agreements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from collaboration agreements	$ 20,756,000	$ 31,096,000
Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from collaboration agreements	9,063,000	4,939,000
Biogen Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from collaboration agreements	10,623,000	19,214,000
Calico Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from collaboration agreements	1,070,000	6,943,000
Betta Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue from collaboration agreements	$ 0	$ 0

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-4

+ Details

Property and equipment - Summary of property and equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Total property and equipment	$ 14,895	$ 15,523
Less: accumulated depreciation	(7,763)	(8,123)
Total property and equipment, net	7,132	7,400
Laboratory equipment
Property Plant And Equipment [Line Items]
Total property and equipment	8,042	8,757
Leasehold improvements
Property Plant And Equipment [Line Items]
Total property and equipment	4,712	4,682
Furniture and fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	1,422	1,181
Office equipment
Property Plant And Equipment [Line Items]
Total property and equipment	621	529
Computer equipment
Property Plant And Equipment [Line Items]
Total property and equipment	98	191
Construction in progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 0	$ 183

Summary of significant accounting policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) segment
Accounting Policies [Abstract]
Number of operating segments \| segment	1
Expected dividend yield \| $	$ 0

Collaboration and license agreements - Allocation of total transaction price and unsatisfied transaction price (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	$ 67,906
Transaction Price Unsatisfied	19,064
Research and development targets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	61,149
Transaction Price Unsatisfied	17,394
Option rights
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction Price Allocated	6,757
Transaction Price Unsatisfied	$ 1,670

Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of financial assets measured at fair value on recurring basis


	Fair Value		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	103,564	$	103,564	$	—	$	—
U.S. Treasury securities	14,972		—		14,972		—
Corporate debt securities	7,588		—		7,588		—
Marketable securities:
Corporate debt securities	128,705		—		128,705		—
U.S. government debt securities	20,428		—		20,428		—
U.S. Treasury securities	5,966		—		5,966		—
Total cash equivalents and marketable securities	$	281,223	$	103,564	$	177,659	$	—

The following table sets forth the fair value of the Company’s financial assets by level within the fair value hierarchy at December 31, 2022 (in thousands):


	Fair Value		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	28,705	$	28,705	$	—	$	—

U.S. Treasury securities	799		—		799		—
Marketable securities:
Corporate debt securities	234,327		—		234,327		—
U.S. government debt securities	47,641		—		47,641		—
U.S. Treasury securities	25,393		—		25,393		—
Total cash equivalents and marketable securities	$	336,865	$	28,705	$	308,160	$	—

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued research and development	$ 11,243	$ 9,824
Accrued compensation and benefits	7,344	6,831
Other	2,043	3,114
Total accrued expenses and other current liabilities	20,630	$ 19,769
Wind down activities	$ 3,100

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Summary of lease costs

The elements of lease costs were as follows (in thousands):


	Years Ended December 31,
	2023		2022
Lease cost:
Operating lease cost	$	10,030	$	10,031
Variable lease cost	1,979		2,026
Sublease income	(2,577)		(1,481)
Total lease cost	$	9,432	$	10,576

Summary of lease term and incremental borrowing rate

The following table summarizes the lease term and incremental borrowing rate applied in arriving at the lease liability:


	As of December 31,
	2023		2022
Remaining lease term	8.1 years		9.1 years
Incremental borrowing rate	5.3	%	5.3	%

Summary of future lease payments

Future lease payments under non-cancelable leases as of December 31, 2023 for each of the years ending December 31 are as follows (in thousands):


Undiscounted lease payments:
2024	$	8,828
2025	9,093
2026	9,366
2027	9,646
2028	11,362
Thereafter	40,751
Total undiscounted lease payments	89,046
Less: imputed interest	(18,070)
Total operating lease liability as of December 31, 2023	$	70,976

Stock-based compensation - Summary of RSU activity (Details)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Restricted stock units
Shares
Outstanding, beginning balance (in shares)	465,291
Granted (in shares)	0
Vested (in shares)	(135,301)
Forfeited (in shares)	(175,990)
Outstanding, ending balance (in shares)	154,000
Weighted-Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 25.09
Granted (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	26.52
Forfeited (in dollars per share) \| $ / shares	28.91
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 19.47
Number of shares retained to cover statutory minimum withholding taxes	17,556
Time-Based Restricted Stock Units
Shares
Outstanding, beginning balance (in shares)	0
Granted (in shares)	824,600
Vested (in shares)	0
Forfeited (in shares)	(74,390)
Outstanding, ending balance (in shares)	750,210
Weighted-Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 0
Granted (in dollars per share) \| $ / shares	5.37
Vested (in dollars per share) \| $ / shares	0
Forfeited (in dollars per share) \| $ / shares	5.67
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 5.35

Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of stock-based compensation expense

Stock-based compensation expense was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Stock-based compensation expense:
Research and development	$	11,826	$	13,108
General and administrative	15,409		16,908
Total stock-based compensation expense	$	27,235	$	30,016

Summary of stock option activity

The following table summarizes the stock option activity under the Company’s equity awards plans for the year ended December 31, 2023:


	Number of Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	6,993,052	$	21.57	7.78	$	1,031
Granted	4,180,270	3.87
Exercised	(13,096)	4.46
Forfeited/expired	(1,685,217)	18.48
Outstanding as of December 31, 2023	9,475,009	$	14.34	7.61	$	8,261
Exercisable as of December 31, 2023	3,838,707	$	20.54	6.68	$	482
Vested and expected to vest as of December 31, 2023	9,475,009	$	14.34	7.61	$	8,261

Other information related to the option activity of the Company was as follows:


	Years Ended December 31,
	2023		2022
Weighted-average fair value of options granted	$	2.84	$	13.44
Intrinsic value of options exercised (in thousands)	$	22	$	1,796

Summary of significant valuation assumptions

The following table summarizes assumptions used in the Black-Scholes option pricing model to determine the fair value of stock options granted to employees:


	Years Ended December 31,
	2023	2022
Expected option life (years)	5.50 - 6.11	5.50 - 6.11
Risk-free interest rate	3.45% - 4.73%	1.47% - 4.22%
Expected volatility	81.99% - 86.15%	81.36% - 88.75%
Expected dividend yield	0.00%	0.00%

Summary of RSU activity

The following table summarizes the activity under the Company’s equity plans with respect to PSUs for the year ended December 31, 2023:


	Shares	Weighted-Average Grant Date Fair Value
Outstanding as of December 31, 2022	465,291	$	25.09
Granted	—	—
Vested (1)	(135,301)	26.52
Forfeited	(175,990)	28.91
Outstanding as of December 31, 2023	154,000	$	19.47

(1) Vested PSUs include 17,556 shares retained by the Company to cover statutory minimum withholding taxes.

The following table summarizes the activity under the Company’s equity plans with respect to RSUs for the year ended December 31, 2023:


	Shares	Weighted-Average Grant Date Fair Value
Outstanding as of December 31, 2022	—	$	—
Granted	824,600	5.37
Vested	—	—
Forfeited	(74,390)	5.67
Outstanding as of December 31, 2023	750,210	$	5.35

As of December 31, 2023, the unrecognized compensation cost related to outstanding RSUs was $3.5 million which is expected to be recognized over a weighted-average period of 3.2 years.

Marketable securities (Tables)

12 Months Ended

Dec. 31, 2023

Marketable Securities [Abstract]

Summary of marketable securities

Marketable securities at December 31, 2023 consisted of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable securities, current:
Corporate debt securities	$	100,903	$	16	$	(221)	$	100,698
U.S. government debt securities	20,457		14		(43)		20,428
U.S. Treasury securities	5,965		1		—		5,966
Marketable securities, non-current
Corporate debt securities	27,901		120		(14)		28,007


Total marketable securities, current and non-current	$	155,226	$	151	$	(278)	$	155,099

Marketable securities at December 31, 2022 consisted of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Marketable securities, current:
Corporate debt securities	$	183,270	$	2	$	(2,068)	$	181,204
U.S. government debt securities	40,986		—		(1,184)		39,802
U.S. Treasury securities	25,650		—		(257)		25,393
Marketable securities, non-current
Corporate debt securities	53,592		2		(471)		53,123
U.S. government debt securities	8,000		—		(161)		7,839

Total marketable securities, current and non-current	$	311,498	$	4	$	(4,141)	$	307,361

Summary of marketable securities in unrealized loss position

Marketable securities in unrealized loss positions as of December 31, 2023 consisted of the following (in thousands, except number of securities):


	Number of Securities	Fair Value		Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months:
Corporate debt securities	64	$	68,563	$	(146)
U.S. government debt securities	9	11,914		(22)

Marketable securities in continuous unrealized loss position for greater than 12 months:
Corporate debt securities	18	22,138		(89)
U.S. government debt securities	3	5,979		(21)

Total marketable securities in unrealized loss position	94	$	108,594	$	(278)

Marketable securities in unrealized loss positions as of December 31, 2022 consisted of the following (in thousands, except number of securities):


	Number of Securities	Fair Value		Gross Unrealized Losses
Marketable securities in continuous unrealized loss position for less than 12 months:
Corporate debt securities	63	$	134,027	$	(1,262)
U.S. government debt securities	6	15,748		(245)
U.S. Treasury securities	4	5,575		(11)
Marketable securities in continuous unrealized loss position for greater than 12 months:
Corporate debt securities	36	82,375		(1,277)
U.S. government debt securities	7	31,892		(1,100)
U.S. Treasury securities	4	19,817		(246)
Total marketable securities in unrealized loss position	120	$	289,434	$	(4,141)

Commitments and contingencies	12 Months Ended
Commitments and contingencies	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Legal proceedings The Company is not currently party to any material legal proceedings. 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.

Summary of significant accounting policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of presentation

The Company has prepared the accompanying consolidated financial statements in conformity with generally accepted accounting principles in the United States of America, or U.S. GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB.

Principles of consolidation

The Company’s consolidated financial statements include the accounts of C4 Therapeutics, Inc. and its wholly owned subsidiary, C4T Securities Corporation, a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation.

Use of estimates

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. This process may result in actual results differing materially from those estimated amounts used in the preparation of the consolidated financial statements if these results differ from historical experience or other assumptions do not turn out to be substantially accurate, even if such assumptions are reasonable when made. Areas where management uses subjective judgement include, but are not limited to, amounts and timing of revenues recognized under the Company’s research and development collaboration arrangements, prepaid and accrued research and development expense, estimates of the useful lives of long-lived assets, assessments of the impairment of long-lived assets, measurement of right-of-use assets and lease liabilities, incremental borrowing rate used in the measurement of lease liability, and valuation and recognition of share-based compensation expense. The Company assesses estimates on an ongoing basis, and bases its estimates on historical experience, known trends and various other assumptions that are believed to be reasonable, the results of which form the basis for making judgements about the carrying values of assets and liabilities. Actual results could materially differ from those estimates.

Segments

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 chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purpose of allocating resources. All of the Company’s long-lived assets are held in the United States.

Cash equivalents

The Company considers all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. The Company’s cash equivalents are measured at fair value on a recurring basis.

Restricted cash

Restricted cash consists of cash placed in a separate restricted bank account as required under the terms of the Company’s lease agreements for its Watertown, Massachusetts facilities, as further described within Note 6, Leases.

Marketable securities

The Company classifies marketable securities with a remaining maturity of greater than three months at the date of purchase as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current assets. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive (loss) income as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income (expense).

Concentrations of credit risk

Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents, marketable securities, and restricted cash. The Company may maintain deposits in financial institutions in excess of government insured limits. The Company believes that it is not exposed to significant credit risk as its deposits are held at financial institutions that management believes to be of high credit quality, and the Company has not experienced any losses on these deposits. Additionally, the Company has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The Company maintains its funds in accordance with its investment policy, which defines allowable investments, specifies credit quality standards and is designed to limit credit exposure to any single issuer.

Fair value of financial instruments

ASC Topic 820, Fair Value Measurement, or ASC 820, establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are those that market participants would use in pricing the asset or

liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier value hierarchy that distinguishes between the following:

•Level 1—Observable inputs that reflect quoted market prices in active markets for identical assets or liabilities in active markets.

•Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable in the marketplace.

•Level 3—Unobservable inputs, which are supported by little or no market activity, and may be developed using estimates of assumptions developed by the Company, which reflect those that a market participant may use.

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company evaluates transfers between levels at the end of each reporting period.

Property and equipment

Property and equipment are recorded at cost, less accumulated depreciation. Expenditures for repairs and maintenance are expensed as incurred. When assets are retired or disposed of, the assets and related accumulated depreciation are derecognized from the accounts, and any resulting gain or loss is included in the determination of net loss.

Depreciation on equipment is calculated using the straight-line method over the estimated useful lives of the assets as follows:


Asset category						Estimated useful life
Laboratory equipment						5 years
Computer equipment						3 years
Office equipment, furniture and fixtures						5 years
Leasehold improvements						Lesser of useful life or remaining lease term

Leases

The Company accounts for leases in accordance with ASC Topic 842, Leases, or ASC 842. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on specific facts and circumstances present, the existence of an identified asset(s), if any, and the Company’s control over the use of the identified asset(s), if applicable. As provided by ASC 842, the Company elected to combine lease and non-lease components as a single component for all leases. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of future lease payments over the expected lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The Company typically only includes an initial lease term in its assessment of a lease arrangement; options to renew a lease are not included in the assessment unless there is reasonable certainty that the Company will renew. The interest rate implicit in lease contracts is typically not readily determinable. As such, in calculating the lease liability, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Lease expense is recognized over the expected lease term on a straight-line basis.

Impairment of long-lived assets

The Company evaluates its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceed the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less costs to sell.

Commitments and contingencies

Liabilities for loss contingencies arising from claims, assessments, litigation, fines and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred.

Revenue recognition

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers, or ASC 606. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services.

The Company enters into collaboration and licensing agreements with strategic partners, which are within the scope of ASC 606, under which it may exclusively license rights to research, develop, manufacture, and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: (1) non-refundable, upfront license fees; (2) reimbursement of certain costs; (3) customer option fees for additional goods or services; (4) development milestone payments; (5) regulatory and commercial milestone payments; and (6) royalties on net sales of licensed products.

In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use its judgment to determine: (a) the number of performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above; (c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above; and (d) the contract term and pattern of satisfaction of the performance obligations under step (v) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied.

Amounts due to the Company for satisfying the revenue recognition criteria or that are contractually due based upon the terms of the collaboration agreements are recorded as accounts receivable in the Company’s consolidated balance sheet. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s consolidated balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion.

Upfront license fees

If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, manufacturing, and commercialization capabilities of the customer; the retention of any key rights by the Company; and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the customer can benefit from a promise for its intended purpose without the receipt of the remaining promises, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company exercises judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Customer options

If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. The Company evaluates the customer options for material rights or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. If an option is not exercised and the target is terminated, the Company will accelerate and recognize all remaining revenue related to the material right performance obligation.

Research and development services

The promises under the Company’s collaboration agreements may include research and development services to be performed by the Company for or on behalf of the customer. Payments or reimbursements resulting from the Company’s research and development efforts are recognized as the services are performed and presented on a gross basis because the Company is the principal for such efforts. Reimbursements from and payments to the customer that are the result of a collaborative relationship with the customer, instead of a customer relationship, such as co-development activities, are recorded as a reduction to research and development expense.

Milestone payments

At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

Research and development expense

Research and development expenses

Research and development costs are expensed as incurred and consist of the costs associated with conducting preclinical studies and clinical trials, which primarily include salaries, stock-based compensation and other employee benefit expenses, lab related supplies and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct research and development activities.

Clinical trial costs are a significant component of the Company's research and development expenses. The Company historically has contracted with third parties that perform various clinical trial activities on behalf of the Company in the ongoing development of the Company's product candidates. As part of the process of preparing the consolidated financial statements, the Company is required to estimate their accrued research and development expenses. The Company makes estimates of the accrued expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known at that time, and include reviewing open contracts and purchase orders, communicating with its personnel to identify services that have been performed on its behalf and estimating the level of service performed and the associated costs incurred for the services when the Company has not yet been invoiced or otherwise notified of the actual costs. If contracted amounts with third parties are modified (for instance, as a result of changes in the clinical trial protocol or scope of work to be performed), the Company will modify the related accruals accordingly on a prospective basis. Revisions in the scope of a contract are charged to expense in the period in which the facts that give rise to the revision become reasonably certain.

In addition, there may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense in which case such amounts are reflected as prepaid expenses and other

current assets. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual or the amount of prepaid expenses accordingly. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized in prepaid expenses and other current assets. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Stock-based compensation

The Company applies ASC Topic 718, Compensation - Stock Compensation, or ASC 718, to account for its stock-based payments. In accordance with the ASC 718, the Company determines whether an award should be classified and accounted for as a liability award or an equity award. All of the Company's grants of stock-based awards to employees were classified as equity awards and are recognized in the Company's financial statements based on the grant date fair value measured using the Black-Scholes option pricing model. The Black-Scholes option pricing model estimates the fair value of the equity award using the expected term, expected volatility, risk-free interest rate, dividend rate, and the fair value of the common stock underlying the stock-based award.

•The Company estimates the expected term using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the contractual term of the option.

•Due to the lack of sufficient company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus.

•The risk-free interest rates for periods within the expected life of the option were based on the U.S. Treasury yield curve in effect during the period the options were granted.

•The expected dividend yield is assumed to be zero as the Company has never paid dividends and currently has no plans to pay any dividends on its common stock.

•The fair value of the common stock underlying shared based awards is the quoted market price of the Company’s common stock on the date of the grant.

•The Company recognizes forfeitures as they occur.

The fair value of the awards are recognized as stock-based compensation expense on a straight-line basis over the requisite service period of the awards, which is generally the vesting period. For awards subject to both performance and service-based vesting conditions, we recognize stock-based compensation expense over the remaining service period if the performance condition is considered probable of achievement using management’s best estimates. Stock-based compensation expense is classified in the consolidated statement of operations and comprehensive loss in the same manner in which the award recipients’ payroll costs are classified or in which the award recipients’ service payments are classified.

A change in any of the terms or conditions of an equity award is accounted for as a modification of the award. Incremental compensation cost is measured as the excess, if any, of the fair value of the modified award over the fair value of the original award immediately before its terms are modified, measured based on the fair value of the awards and other pertinent factors at the modification date. For vested awards, the Company recognizes incremental compensation cost in the period the modification occurs. For unvested awards, the Company recognizes the expense over the remaining requisite service period, the sum of the incremental compensation cost and the remaining unrecognized compensation cost for the original award on the modification date. If the fair value of the modified award is lower than the fair value of the original award immediately before modification, the minimum compensation cost the Company recognizes is the cost of the original award.

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 consequence of events that have been recognized in the consolidated financial statements or the Company’s tax returns. Under this method, deferred tax assets and liabilities are determined based on the differences between the consolidated financial statements 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.

The Company evaluates its uncertain tax positions using the provisions of ASC Topic 740, Income taxes, or ASC 740, which prescribes a recognition threshold that a tax position is required to meet before being recognized in the consolidated financial statements by using a "more-likely-than-not" criteria for financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, which are considered appropriate as well as the related net interest and penalties.

Comprehensive loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss includes net loss as well as other changes in stockholders’ equity which includes certain changes in equity that are excluded from net loss. The Company’s only element of other comprehensive income is unrealized gains and losses on marketable securities.

Net loss per share

Basic and diluted net loss per share are computed using the weighted-average number of shares of common stock outstanding for the period. The Company computes diluted (loss) earnings per share after giving consideration to the dilutive effect of stock options and unvested restricted stock that are outstanding during the period, except where such securities would be anti-dilutive.

Common stock equivalent shares are excluded from the computation of diluted net loss per share if their effect is antidilutive. In periods in which the Company reports a net loss, diluted net loss per share is generally the same as basic net loss per share since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

Going concern

At each reporting period, the Company evaluates whether there are conditions or events 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. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash, cash equivalent, and marketable securities balances.

Recently issued accounting standards

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. or ASU 2023-09. ASU 2023-09 requires a company's annual financial statements to include consistent categories and greater disaggregation of information in the rate reconciliation, and income taxes paid disaggregated by jurisdiction. ASU 2023-09 is effective for the Company’s annual reporting periods beginning after December 15, 2025. Adoption is either with a prospective method or a fully retrospective method of transition. Early adoption is permitted. The Company is currently evaluating the effect that adoption of ASU 2023-09 will have on its consolidated financial statements.

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2021		48,688,875
Beginning balance at Dec. 31, 2021	$ 389,606	$ 5	$ 658,091	$ (775)	$ (267,715)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options and release of stock units (in shares)		235,450
Exercise of stock options and release of stock units	777		777
Issuance of common stock under the 2020 ESPP (in shares)		31,402
Issuance of common stock under the 2020 ESPP	372		372
Stock-based compensation	29,858		29,858
Unrealized gain (loss) on marketable securities	(3,362)			(3,362)
Net loss	(128,175)				(128,175)
Other (in shares)		10,489
Other	158		158
Ending balance (in shares) at Dec. 31, 2022		48,966,216
Ending balance at Dec. 31, 2022	289,234	$ 5	689,256	(4,137)	(395,890)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to the at-the-market equity program, net (in shares)		11,186,142
Issuance of common stock pursuant to the at-the-market equity program, net	57,673	$ 1	57,672
Exercise of stock options and release of stock units (in shares)		13,096
Exercise of stock options and release of stock units	58		58
Issuance of common stock upon vesting of restricted stock units, net of shares repurchased for tax withholding (in shares)		117,745
Issuance of common stock upon vesting of restricted stock units, net of shares repurchased for tax withholding	(110)		(110)
Issuance of common stock under the 2020 ESPP (in shares)		133,784
Issuance of common stock under the 2020 ESPP	368		368
Stock-based compensation	27,235		27,235
Unrealized gain (loss) on marketable securities	4,010			4,010
Net loss	(132,493)				(132,493)
Other (in shares)		50,205
Other	139		139
Ending balance (in shares) at Dec. 31, 2023		60,467,188
Ending balance at Dec. 31, 2023	$ 246,114	$ 6	$ 774,618	$ (127)	$ (528,383)

Net loss per share - Schedule of basic and diluted loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net loss	$ (132,493)	$ (128,175)
Denominator:
Weighted-average number of shares - basic (in shares)	49,640,505	48,861,665
Weighted-average number of shares - diluted (in shares)	49,640,505	48,861,665
Net loss per share — diluted (in dollars per share)	$ (2.67)	$ (2.62)
Net loss per share — basic (in dollars per share)	$ (2.67)	$ (2.62)

- 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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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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+ Details

- Definition

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

+ References

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+ Details

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 126,590	$ 29,754
Marketable securities, current	127,091	246,399
Accounts receivable	11,799	1,473
Prepaid expenses and other current assets	5,709	9,931
Total current assets	271,189	287,557
Marketable securities, non-current	28,008	60,962
Property and equipment, net	7,132	7,400
Right-of-use asset	63,956	70,116
Restricted cash	3,443	3,279
Other assets	2,723	1,526
Total assets	376,451	430,840
Current liabilities:
Accounts payable	1,446	1,172
Accrued expenses and other current liabilities	20,630	19,769
Deferred revenue, current	15,471	16,618
Operating lease liability, current	5,219	4,700
Long-term debt, net of debt discount—related party, current	0	2,287
Total current liabilities	42,766	44,546
Deferred revenue, net of current	21,814	16,895
Operating lease liability, net of current	65,757	70,970
Long-term debt, net of debt discount—related party, net of current	0	9,195
Total liabilities	130,337	141,606
Commitments and contingencies (See Note 6 and Note 9)
Stockholders’ equity:
Preferred stock, par value of $0.0001 per share; 10,000,000 shares authorized, and no shares issued or outstanding as of December 31, 2023 and 2022, respectively	0	0
Common stock, par value of $0.0001 per share; 150,000,000 shares authorized, and 60,467,188 and 48,966,216 shares issued and outstanding as of December 31, 2023 and 2022, respectively	6	5
Additional paid-in capital	774,618	689,256
Accumulated other comprehensive loss	(127)	(4,137)
Accumulated deficit	(528,383)	(395,890)
Total stockholders’ equity	246,114	289,234
Total liabilities and stockholders’ equity	$ 376,451	$ 430,840

Income taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income taxes

Income tax (benefit) expense consists of the following (in thousands):


	Years Ended December 31,
	2023		2022
Current tax provision:
Current federal provision	$	—	$	—
Current state provision	76		—
Current foreign provision	1,204		—
Total current provision	1,280		—
Deferred tax provision:
Deferred federal provision	—		—
Deferred state provision	—		—
Deferred foreign provision	—		—
Total tax provision	$	1,280	$	—

Tax rate reconciliation

A reconciliation of the expected income tax (benefit) expense computed at the statutory federal rate to income taxes as reflected in the consolidated financial statements was as follows:


	Years Ended December 31,
	2023		2022
Income tax benefit computed at federal statutory tax rate	21.0	%	21.0	%
State tax—net of federal	4.2	%	8.0	%
Federal credits	3.5	%	1.4	%
State credits	1.4	%	0.1	%
Other permanent differences	(0.2)	%	(0.8)	%
Withholding tax	(0.9)	%	—	%
Stock-based compensation	(2.8)	%	(3.0)	%


Valuation allowance	(27.2)	%	(26.7)	%
Total	(1.0)	%	—	%

The Company's effective tax rate as of December 31, 2023, was impacted by the Chinese withholding tax obligation related to the upfront and milestone payments received in connection with the Betta License agreement (see Note 8). This resulted in a tax provision of $1.2 million and effective tax rate of (1.0)% for the ended December 31, 2023.

Significant components of deferred taxes

Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and (b) operating losses and tax

credit carryforwards. Significant components of the Company’s deferred tax assets and deferred tax liabilities were as follows (in thousands):


	As of December 31,
	2023		2022
Deferred tax assets:
Net operating losses	$	61,036	$	54,300
Capitalized research and experimental expenditures	51,401		27,568
Operating lease liability	20,611		21,443
R&D and investment tax credits	18,049		11,519
Stock-based compensation	9,061		6,296
Deferred revenue	3,881		8,457
Foreign tax credit	1,204		—
Capitalized start-up costs	555		699
Unrealized gain/loss	—		1,090
Other	27		354
Total gross deferred tax assets	165,825		131,726
Deferred tax liabilities:
Right-of-use asset	(18,573)		(19,868)
Fixed assets	(1,663)		(1,738)

Less: valuation allowance	(145,589)		(110,120)
Net deferred taxes	$	—	$	—

The Company has evaluated the positive and negative evidence bearing upon the realizability of the deferred tax assets. As of December 31, 2023 and 2022, based on the Company’s historical operating losses, the Company has concluded that it is more-likely-than-not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for the deferred tax assets as of December 31, 2023 and 2022. The valuation allowance for deferred tax assets as of December 31, 2023 and 2022 was $145.6 million and $110.1 million, respectively. The net valuation allowance increased $35.5 million and $34.7 million during the years ended December 31, 2023 and 2022, respectively. The change during the year ended December 31, 2023 was primarily due to the increase in net operating loss and tax credits carryforward, capitalization of research and experimental expenditures, and a decrease in deferred revenue recognized during the year.

As of December 31, 2023 and 2022, the Company had $214.9 million and $171.6 million gross United States federal net operating loss, or NOL, carryforwards, respectively, which may be available to offset future taxable income. The Tax Cuts and Jobs Act, or TCJA, which was enacted in December 2017, will generally allow federal losses generated after 2017 to be carried over indefinitely, but will generally limit the NOL deduction to the lesser of the NOL carryover or 80% of a corporation’s taxable income (subject to Section 382 of the Internal Revenue Code of 1986, as amended, or IRC). In addition, there will be no carryback for losses generated after 2017. Losses generated prior to 2018 will generally be deductible to the extent of the lesser of a corporation’s NOL carryover or 100% of a corporation’s taxable income and be available for twenty years from the period the loss was generated. For U.S. federal income tax purposes, the Company has federal NOLs generated after 2017 of $214.9 million, which do not expire. The Company does not have any available NOLs generated prior to 2019 as they were fully utilized in 2019. The Coronavirus Aid, Relief and Economic Security Act, or CARES Act, temporarily allows the Company to carryback net operating losses arising in 2018, 2019 and 2020 to the five prior tax years. In addition, net operating losses generated in these years could fully offset prior year taxable income without the 80% of the taxable income limitation under the TCJA.

As of December 31, 2023 and 2022, the Company has total gross United States state net operating loss carryforwards of $315.3 million and $273.6 million, respectively, which may be available to offset future taxable income that expire at various dates through 2043.

At December 31, 2023 and 2022, the Company has United States federal research credit carryforwards of $12.6 million and $9.1 million, respectively, which are available to offset future federal income tax liabilities, which expire at various dates through 2043. At December 31, 2023 and 2022, the Company has United States state research credit carryforwards of $5.2

million and $2.9 million, respectively, which are available to reduce future tax liabilities which expire at various dates through 2038.

Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the IRC, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. In 2022, the Company completed a study of ownership changes from inception through December 31, 2020, to assess whether an ownership change has occurred or whether there have been multiple ownership changes since its formation. The result of this study indicated that the Company experienced ownership changes as defined by Section 382 of the Internal Revenue Code, however there are no net operating loss carryforwards that will be limited and expire unused as a result of such ownership changes. Given the continued loss position, the Company has not currently undertaken an analysis for IRC Section 382 purposes of any activities post December 31, 2020. A full valuation allowance has been provided against the Deferred Tax Assets related to the Company’s net operating loss and tax credit carryforwards and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance.

The Company will recognize interest and/or penalties related to unrecorded tax benefits in income tax expense as they arise. As of December 31, 2023 and 2022, the Company had no accrued interest or penalties related to unrecorded tax benefits.

The Company files income tax returns in the United States, California, Florida, and Massachusetts. The federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2020 through present. To the extent that the Company has tax attribute carryforwards, the tax years in which the attributes were generated may still be adjusted upon examination by the Internal Revenue Services or State tax authorities to the extent utilized in a future period. The Company is not currently under examination by any tax authorities.

- 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

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+ Details

Collaboration and license agreements

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaboration and license agreements

Merck License and Collaboration Agreement

On December 11, 2023, the Company entered into an exclusive license and collaboration agreement with Merck, or the Merck Agreement, to develop degrader-antibody conjugates, or DACs, an emerging modality designed to selectively target and neutralize disease-causing proteins in cancer cells.

Under the terms of the Merck Agreement, the Company received a $10.0 million upfront payment in January 2024. The Company and Merck will collaborate to develop DACs directed to an initial undisclosed oncology target that is exclusive to the collaboration. For DACs directed to this initial target, the Company is eligible to receive milestone payments totaling approximately $600 million, as well as tiered royalties on future sales. The agreement also provides Merck with the option to extend the collaboration to include three additional targets that would be exclusive to the collaboration, which could yield option exercise payments as well as potential milestones and royalties. If Merck exercises all of its options to extend the collaboration, the Company would be eligible to receive up to approximately $2.5 billion in potential payments across the entire collaboration.

The collaboration is managed by a joint research committee, or JRC, which is comprised of representatives from both Merck and the Company. Each party also has various termination rights under certain circumstances, including but not limited to regulatory safety stoppages, patent challenges, or a material breach by the other party, subject to certain conditions. Termination of the agreement is subject to the determination of the JRC.

Merck Agreement Accounting

The Company identified one performance obligation at the outset of the Merck Agreement, which consists of: (1) the exclusive license and (2) the research activities for the initial undisclosed oncology target and the joint research plan. The Company determined that the license and research activities were not distinct from one another, as the license has limited value without the performance of the research activities by the Company. Participation on the Merck JRC to oversee the research activities and the technology transfer associated with the Merck Agreement were determined to be quantitatively and qualitatively immaterial and therefore are excluded from performance obligations. The Company recognizes the transaction price allocated to this performance obligation as the research and development services are provided, using an input method, in proportion to costs incurred to date for each research development target as compared to total costs incurred and expected to be incurred in the future to satisfy the underlying obligation. The transfer of control occurs over this period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation.

As of December 31, 2023, total transaction price of $10.0 million is allocated to the research and development services performance obligation and $10.0 million of the allocated transaction price remains unsatisfied.

Amounts due to the Company that have not yet been received are recorded as accounts receivable and amounts received that have not yet been recognized as revenue are recorded as deferred revenue on the Company’s consolidated balance sheet.

Betta Pharma License and Collaboration Agreement

On May 29, 2023, the Company entered into a license and collaboration agreement, or the Betta Pharma License Agreement, with Betta Pharma to collaborate on the development and commercialization of CFT8919 in Greater China,

comprised of mainland China, Hong Kong SAR, Macau SAR and Taiwan, with the Company retaining rights to CFT8919 in the rest of the world other than Greater China, or the C4T Territory.

Under the terms of the Betta Pharma License Agreement, the Company grants Betta Pharma an exclusive license under certain of the Company's intellectual property rights to develop, manufacture and commercialize CFT8919 for all uses in humans in Greater China. Betta Pharma is responsible for all development, regulatory approval, manufacturing and commercialization costs in Greater China except where Betta Pharma acts as the Company's agent in Greater China in connection with a global trial sponsored by the Company. As part of the collaboration, Betta Pharma made an upfront cash payment of $10.0 million to the Company and has agreed to make up to $357.0 million in aggregate milestone payments, plus tiered royalties on net sales of CFT8919 in Greater China. These payments are subject to a withholding tax by the State Taxing Authority of the People's Republic of China. Royalties payable from Betta Pharma to the Company range from low to mid double-digit percent, subject to certain reductions under certain circumstances as described in the Betta Pharma License Agreement. In addition, as part of the collaboration, the Company has agreed to make milestone payments to Betta Pharma of up to $40.0 million following the Company's receipt of approval of a New Drug Application for CFT8919 from the FDA, with the milestone amount based on the percentage of patients in contemplated clinical trials that were enrolled by Betta Pharma and the line of therapy of the approval. In addition, the Company has agreed to pay Betta Pharma tiered royalties on net sales of CFT8919 in the C4T Territory in the low single digit percent range, subject to reductions under certain circumstances as described in the Betta Pharma License Agreement.

In connection with the execution of the Betta Pharma License Agreement, the Company, Betta Pharma, and an affiliate of Betta Pharma, (Betta Investment (Hong Kong) Limited, or Betta Investment), entered into a stock purchase agreement dated May 29, 2023, or the Betta Stock Purchase Agreement, and together with the Betta Pharma License Agreement, or the Betta Agreements, pursuant to which Betta Investment agreed to purchase 5,567,928 shares of the Company's common stock, or the Shares, for an aggregate purchase price of approximately $25.0 million, or $4.49 per share, which represented a 25% premium over the 60-trading-day volume weighted average closing price as of two trading days prior to the effective date of the Betta Stock Purchase Agreement. The Betta Stock Purchase Agreement has certain restrictions customary to agreements of this nature. As the closing under the Betta Stock Purchase Agreement did not occur until January 4, 2024, no activity under the Betta Stock Purchase Agreement was recorded as of December 31, 2023.

The collaboration is managed by a joint steering committee, which is composed of representatives from both Betta Pharma and the Company. Following the completion of the dose escalation phase of the Phase 1 trial of CFT8919, Betta Pharma may terminate the Betta Pharma License Agreement for convenience upon at least 90 days’ prior written notice. Each party also has various termination rights under certain circumstances, including but not limited to regulatory safety stoppages, patent challenges, or a material breach by the other party, subject to certain conditions.

Betta Agreements accounting

The Company expects to recognize revenue under the Betta Agreements from one type of arrangement, the licensing agreement. The Betta Agreements will consist of the following activities: (1) license of intellectual property, (2) clinical manufacturing supply agreement, and (3) manufacturing technology transfer, and (4) commercial manufacturing supply agreement. As of December 31, 2023, the total transaction price is currently $12.0 million, consisting of the $10.0 million upfront cash consideration and a $2.0 million milestone achieved in December 2023 under the Betta Pharma License Agreement. Revenue recognition associated with the Betta Agreements is expected to commence upon the delivery of clinical supply under the clinical manufacturing supply agreement, which has not been executed as of December 31, 2023. The Company has collected a net amount of $9.0 million from the upfront payment from Betta Pharma, after making the related withholding tax payment of $1.0 million to the Chinese tax authorities (See Note 12). No revenue has been recognized as of December 31, 2023, in respect of the transaction price allocated to the Betta Agreements.

Roche Collaboration and License Agreement

In March 2016, the Company entered into a license agreement with Roche, which was amended in June 2016 and again in March 2017. The Company and Roche amended and restated that agreement (as so amended) in December 2018. This amended and restated agreement is referred to as the Roche Agreement. Under the Roche Agreement, the Company and Roche agreed to collaborate in the research, development, manufacture and commercialization of target-binding degrader medicines using the Company’s proprietary TORPEDO platform for the treatment of cancers and other indications. Under the Roche Agreement, the Company may elect to opt into certain co-development rights, in which case the Company will

receive an increased royalty rate on future product sales from products directed to that target. In addition, if the Company opts into certain co-detailing rights, it is also entitled to reimbursement of certain commercialization costs. Upon entry into the Roche Agreement, the Company received additional upfront consideration of $40.0 million.

In November 2020, the Company signed a further amendment, the effect of which was to provide that the parties would develop up to five potential targets, with Roche maintaining its option rights to license and commercialize products directed to those targets. The November 2020 amendment also provides a mechanism through which the Company and Roche can mutually agree to terminate the Roche Agreement on a target-by-target basis by the entry into a Mutual Target Termination Agreement. Upon the entry into a Mutual Target Termination Agreement, the Roche Agreement provides that all rights and responsibilities for know-how and other intellectual property in support of products that use inhibition as their mode of action revert to Roche and all rights and responsibilities for know-how and other intellectual property in support of products that use degradation as their mode of action revert to the Company. In support of this allocation of rights, Roche provides the Company, and the Company provides Roche, with a perpetual irrevocable, fully paid up, exclusive (even as to party granting the license), sublicensable (including in multiple tiers) license to the patents and know-how that are allocated to a party under a Mutual Target Termination Agreement. As the research activities with Roche have progressed and evolved over time, there are now two targets on which the parties continue to collaborate, with Roche maintaining its option rights to license and commercialize products directed to those two targets. In December 2023, the Company signed a second amendment to the Roche Agreement, the effect of which was to update the terms of the agreement as it pertains to the two targets on which the parties continue to collaborate. Under the second amendment to the Roche Agreement, Roche retains its option rights to license and commercialize products directed to those targets but the timing of its option rights are adjusted to begin upon Roche's receipt of the dose range finding data package. There was no material impact to the accounting in 2023 as a result of the second amendment to the Roche Agreement.

Under the Roche Agreement, as amended, the Company receives annual research plan payments of $1.0 million for each active research plan. For the two targets that remain under collaboration among the parties, Roche is required to pay the Company fees of $2.0 million upon the progression of targets to the lead series identification achievement phase. In the event Roche exercises its option rights as to one of these targets, Roche is required to pay the Company an option exercise fee of $8.0 million.

Under the Roche Agreement, as amended, for each target option exercised by Roche, the Company is eligible to receive milestone payments up to $273.0 million upon the achievement of certain development milestones with respect to corresponding products, subject to certain reductions and exclusions based on intellectual property coverage. Roche is also required to pay the Company up to $150.0 million per target in one-time sales-based milestone payments upon the achievement of specified levels of net sales of a product directed to such target. Finally, Roche is required to pay the Company tiered royalties ranging from the mid-single digits to mid-teen percentages on net sales of products sold by Roche pursuant to its exercise of its option rights, subject to certain reductions. For sales of products for which the Company exercises its co-development right, the applicable royalty rates will be increased by a low-single digit percentage.

The collaboration is managed by a joint research committee, or JRC. The Company has control over the JRC prior to Roche’s exercise of its option rights as to a particular target, with Roche assuming control of the JRC thereafter, Roche may terminate the Roche Agreement on a target-by-target or product-by-product basis under several scenarios, upon at least 90 days’ prior written notice.

Roche Agreement accounting

At commencement, the Company identified twelve performance obligations within the Roche Agreement, represented by the six potential research and development targets then included in the collaboration and the option rights held by Roche for each of those six targets. A non-exclusive royalty-free license to use the Company’s intellectual property to conduct research and development activities, as well as participation on the JRC, were identified as promised services. However, the Company determined that the research and development license and research and development services were not distinct from one another, and participation on the JRC was determined to be quantitatively and qualitatively immaterial.

The total transaction price of the Roche Agreement is allocated to the performance obligations based on their relative standalone selling price. The allocated transaction price is recognized as revenue from collaboration agreements in one of two ways:

•Research and development targets: The Company recognizes the portion of the transaction price allocated to each of the research and development performance obligations as the research and development services are provided, using an input method, in proportion to costs incurred to date for each research development target as compared to total costs incurred and expected to be incurred in the future to satisfy the underlying obligation

related to said research and development target. The transfer of control occurs over this period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation.

•Option rights: The transaction price allocated to the options rights, which are considered material rights, is recognized in the period that Roche elects to exercise or elects to not exercise its option right to license and commercialize the underlying research and development target.

The following table summarizes the allocation of the total transaction price to the identified performance obligations under the arrangement, and the amount of the transaction price unsatisfied as of December 31, 2023 (in thousands):


	Transaction Price Allocated		Transaction Price Unsatisfied
Performance obligations:
Research and development targets	$	61,149	$	17,394
Option rights	6,757		1,670
Total	$	67,906	$	19,064

Biogen Collaboration Research and License Agreement

In December 2018, the Company entered into a collaboration research and license agreement, or the Biogen Agreement, with Biogen. In February 2020, the Company and Biogen amended the Biogen Agreement to provide further clarity around Biogen’s ownership of target binding moieties (which are portions of molecules), and any related intellectual property that are directed at or bind to collaboration targets. This amendment further provided that Biogen licenses to the Company rights to use these Biogen target binding moieties and any related intellectual property as needed in order to conduct the research and development activities contemplated under the Biogen Agreement. Pursuant to the terms of the Biogen Agreement, the Company and Biogen agreed to collaborate on research activities to develop novel treatments for neurological conditions such as Alzheimer's disease and Parkinson's disease through medicines that rely on target protein degradation, or TPD, as their mode of action, all of which are created using the Company’s degrader technology. Under the terms of the Biogen Agreement, the Company was engaged to develop TPD therapeutics that utilize degrader technology for up to five target proteins over a period of 54 months, ending in June 2023. On a target-by-target basis, after successful completion of a defined target evaluation period, Biogen assumes full rights and responsibility for continued development of each target.

In exchange for the non-exclusive research license from Biogen, as well as a $45.0 million nonrefundable upfront payment, the Company has granted a license to develop, commercialize, and manufacture products related to each of the targets (which is contingent on not cancelling the agreement), performs initial research services for drug discovery, has provided a non-exclusive research and commercial license to its intellectual property, and participates on the joint steering committee, or the Biogen JSC. The Company was also obligated to participate in early research activities for other potential targets or sandbox activities, at Biogen’s election up to a maximum amount; any work performed for these services is reimbursed by Biogen, and Biogen reimburses the Company for certain FTE costs. The Company’s obligations under the sandbox activities were completed as of August 31, 2021. For any target, following the achievement of development candidate criteria and prior to any IND-enabling study, Biogen will bear all costs and expenses of and will have sole discretion and decision-making authority with respect to the performance of further activities with respect to any degrader under development under the Biogen Agreement and all products that incorporate that degrader. Biogen is also required to pay the Company up to $35.0 million per target in development milestones and $26.0 million per target in one-time sales-based payments for the first product to achieve certain levels of net sales. In addition, Biogen is required to pay the Company royalties on a licensed product-by-licensed product basis, on worldwide net product sales. All milestone and sales-based payments are made after the Company has met the defined criteria in the joint research plan for that target, at which time Biogen will have control of the products related to the targets for commercialization; the receipt of these payments is contingent on the further development of products directed to the targets to commercialization by Biogen, without any additional research and development efforts from the Company.

The collaboration is managed by the Biogen JSC, which Biogen has control over, and Biogen may terminate the Biogen Agreement on a target-by-target or product-by-product basis under several scenarios, upon at least 90 days’ prior written notice.

Biogen Agreement accounting

The Company recognizes revenue under the Biogen Agreement for research and development services as follows:

•Research and development services: The Company identified one performance obligation at the outset of the Biogen Agreement, representing a combined performance obligation consisting of (1) the licenses, (2) the research activities for the target evaluation phase for all five targets and (3) the joint research plan phase for each target. The Company determined that the licenses and research activities were not distinct from one another, as the licenses have limited value without the performance of the research activities by the Company. Participation on the Biogen JSC to oversee the research activities and the technology transfer associated with the Biogen License Agreement were determined to be quantitatively and qualitatively immaterial and therefore are excluded from performance obligations. The Company recognizes the transaction price allocated to this performance obligation as the research and development services are provided, using an input method, in proportion to costs incurred to date for each research development target as compared to total costs incurred and expected to be incurred in the future to satisfy the underlying obligation related to said research and development target. The transfer of control occurs over this period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation.

As of December 31, 2023, total transaction price of $55.0 million is allocated to the research and development services performance obligation and $0.8 million of the allocated transaction price remains unsatisfied.

Amounts due to the Company that have not yet been received are recorded as accounts receivable and amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet.

Calico Collaboration and License Agreement

In March 2017, the Company entered into a collaboration and license agreement, or the Calico Agreement, with Calico whereby the Company and Calico agreed to collaborate to develop and commercialize small molecule protein degraders for diseases of aging, including cancer, for a five-year period ending in March 2022. In August 2021, the Company provided Calico with an option to extend the research term with respect to a certain program for up to a one-year period ending in March 2023. In September 2021, Calico exercised the option resulting in a $1.0 million extension payment to the Company. In addition, Calico will continue to reimburse the Company for a number of FTEs, depending on the stage of the research, at specified market rates. As of March 13, 2023, the research term of the Calico Agreement has expired, and the Company's research activities associated with the agreement are substantially complete.

Under the Calico Agreement, Calico paid an upfront amount of $5.0 million and certain annual payments totaling $5.0 million through June 30, 2020 and pays target initiation fees and reimburses the Company for a number of FTEs, depending on the stage of the research, at specified market rates. For each target, the Company is eligible to receive up to $132.0 million in potential development and commercial milestone payments, on sales of all products resulting from the collaboration efforts. Calico is also required to pay the Company up to $65.0 million in one-time sales-based payments for the first product to achieve certain levels of net sales. In addition, Calico is required to pay the Company royalties, at percentages in the mid-single digits, on a licensed product-by-licensed product basis, on worldwide net product sales. All milestone and sales-based payments are made after the Company has met the defined criteria in the joint research plan for that target, at which time Calico will have control of the products related to targets for commercialization; the receipt of these payments by the Company is contingent on the further development of the targets to commercialized products by Calico, without any additional research and development efforts required by the Company.

As of December 31, 2023, the total transaction price of $13.0 million was allocated to the research and development services performance obligation and the transaction price has been fully allocated and satisfied.

Amounts due to the Company that have not yet been received are recorded as accounts receivable on the Company’s condensed consolidated balance sheet.

Summary of revenue recognized from collaboration agreements

Revenue from collaboration agreements was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Revenue from collaboration agreements:
Roche Agreement	$	9,063	$	4,939
Biogen Agreement	10,623		19,214
Calico Agreement	1,070		6,943
Betta Agreement	—		—
Total revenue from collaboration agreements	$	20,756	$	31,096

Supplemental information related to the collaboration and license agreements consisted of the following in the Company’s consolidated balance sheet as of December 31, 2023 (in thousands):


	Accounts Receivable		Deferred Revenue, Current		Deferred Revenue, Net of Current		Deferred Revenue, Total
Supplemental information:
Roche Agreement	$	—	$	2,667	$	11,814	$	14,481
Betta Agreement	1,799		4,000		8,000		12,000
Merck Agreement	10,000		8,000		2,000		10,000
Biogen Agreement	—		804		—		804

Total	$	11,799	$	15,471	$	21,814	$	37,285

Supplemental information related to the collaboration and license agreements consisted of the following in the Company’s consolidated balance sheet as of December 31, 2022 (in thousands):


	Accounts Receivable		Deferred Revenue, Current		Deferred Revenue, Net of Current		Deferred Revenue, Total
Supplemental information:
Roche Agreement	$	417	$	4,649	$	16,895	$	21,544
Biogen Agreement	—		11,427		—		11,427
Calico Agreement	1,056		542		—		542
Total	$	1,473	$	16,618	$	16,895	$	33,513

Supplemental financial information related to the collaboration and license agreements are (in thousands):


	Years Ended December 31,
	2023		2022
Revenue recognized that was included in the contract liability at the beginning of the period	$	20,185	$	25,412
Revenue recognized from performance obligations fully or partially satisfied in previous periods	43		518

As of December 31, 2023, the aggregate amount of the transaction price allocated to performance obligations under the Roche Agreement, Betta Agreements, Merck Agreement, and the Biogen Agreement that are partially unsatisfied was $41.9 million.

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Audit Information [Abstract]
Auditor firm ID	185
Auditor name	KPMG LLP
Auditor location	Boston, MA, United States

Subsequent events (Details) - Subsequent event $ in Millions	Jan. 09, 2024 USD ($)
Subsequent Event [Line Items]
Percent reduction in workforce	30.00%
Expected restructuring charges	$ 2.7

Collaboration and license agreements - Narrative (Details)			1 Months Ended						12 Months Ended		40 Months Ended
	Dec. 11, 2023 USD ($) target	May 29, 2023 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Aug. 31, 2021	Nov. 30, 2020 USD ($) target	Feb. 29, 2020 USD ($) protein	Dec. 31, 2018 USD ($) target performanceObligation	Mar. 31, 2017 USD ($)	Dec. 31, 2023 USD ($) target performance_obligation	Dec. 31, 2022 USD ($)	Jun. 30, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract with customer, liability									$ 37,285,000	$ 33,513,000
Number of performance obligations \| performanceObligation							12
Revenue from collaboration agreements									20,756,000	31,096,000
Revenue recognized that was included in the contract liability at the beginning of the period									20,185,000	25,412,000
Transaction price allocated to performance obligation									67,906,000
Foreign Tax Authority
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments for tax withholdings									1,000,000
Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice period for termination of agreement		90 days
Merck Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 10,000,000
Option to include number of additional targets \| target	3
Potential proceeds from collaboration	$ 2,500,000,000
Contract with customer, liability									10,000,000
Merck Agreement \| Research and development milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive	$ 600,000,000
Betta Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment		$ 10,000,000							9,000,000
Contract with customer, liability									12,000,000
Stock repurchase program, number of shares authorized to be repurchased (in shares) \| shares		5,567,928
Stock repurchase program, authorized amount		$ 25,000,000
Share price (in dollars per share) \| $ / shares		$ 4.49
Stock repurchase program, premium percentage		25.00%
Regulatory milestone achieved									2,000,000
Revenue from collaboration agreements									$ 0	$ 0
Betta Agreement \| Research and development milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive		$ 357,000,000
Betta Agreement \| Drug Application Approval
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive		$ 40,000,000
Restated Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional upfront consideration received							$ 40,000,000
Number of potential targets \| target					5		6
Number of targets \| target					2				2
Annual research plan payments receivables					$ 1,000,000
Option exercise fees					8,000,000
Restated Roche Agreement \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice period for termination of agreement									90 days
Restated Roche Agreement \| Maximum \| Research, development and commercial milestone payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive					273,000,000
Restated Roche Agreement \| Maximum \| One-time sales-based payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive					150,000,000
Restated Roche Agreement \| Lead series identification achievement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees					$ 2,000,000
Biogen Research and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research agreement, period						54 months
Nonrefundable upfront payment						$ 45,000,000
Biogen Research and License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targeted protein degradation \| protein						5
Biogen Research and License Agreement \| Maximum \| Research and development milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						$ 35,000,000
Biogen Research and License Agreement \| Maximum \| One-time sales-based payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						$ 26,000,000
Biogen License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets \| target									5
Number of performance obligations \| performance_obligation									1
Biogen License Agreement \| Research and development services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized that was included in the contract liability at the beginning of the period									$ 55,000,000
Transaction price allocated to performance obligation									$ 800,000
Biogen License Agreement \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice period for termination of agreement									90 days
Calico License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment											$ 5,000,000
Research term								5 years
Research extend term				1 year
Amount payable for extend research term option			$ 1,000,000
Annual payments											$ 5,000,000
Calico License Agreement \| Research and development services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized that was included in the contract liability at the beginning of the period									$ 13,000,000
Calico License Agreement \| Maximum \| One-time sales-based payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received								$ 65,000,000
Calico License Agreement \| Maximum \| Potential research, development and commercial milestone payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received								$ 132,000,000
Calico License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to performance obligation									$ 41,900,000

Long-term debt and warrant – related party – related party - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Jun. 30, 2020	Jun. 05, 2020
Long Term Debt And Warrant Liability [Line Items]
Loss on early extinguishment of debt	$ 621	$ 0
Interest expense	$ 1,000	$ 1,500
Credit Agreement with Perceptive Life Sciences Master Fund LTD \| Term Loan
Long Term Debt And Warrant Liability [Line Items]
Aggregate principal borrowing amount				$ 20,000
Credit Agreement with Perceptive Life Sciences Master Fund LTD \| Term Loan \| Tranche one
Long Term Debt And Warrant Liability [Line Items]
Aggregate principal borrowing amount				12,500
Amount withdrawn			$ 12,500
Credit Agreement with Perceptive Life Sciences Master Fund LTD \| Term Loan \| Tranche two
Long Term Debt And Warrant Liability [Line Items]
Aggregate principal borrowing amount				$ 7,500

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Leases - Summary of lease costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease cost	$ 10,030	$ 10,031
Variable lease cost	1,979	2,026
Sublease Income	(2,577)	(1,481)
Total lease cost	$ 9,432	$ 10,576

Property and equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and equipment

Property and equipment consisted of the following (in thousands):


	As of December 31,
	2023		2022
Property and equipment
Laboratory equipment	$	8,042	$	8,757
Leasehold improvements	4,712		4,682
Furniture and fixtures	1,422		1,181
Office equipment	621		529
Computer equipment	98		191
Construction in progress	—		183
Total property and equipment	14,895		15,523
Less: accumulated depreciation	(7,763)		(8,123)
Total property and equipment, net	$	7,132	$	7,400

Depreciation expense related to property and equipment was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Depreciation expense	$	1,578	$	1,676

Summary of significant accounting policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of significant accounting policies

Basis of presentation

Principles of consolidation

Use of estimates

Segments

Cash equivalents

Restricted cash

Marketable securities

Concentrations of credit risk

Fair value of financial instruments

•Level 1—Observable inputs that reflect quoted market prices in active markets for identical assets or liabilities in active markets.

•Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable in the marketplace.

Property and equipment

Depreciation on equipment is calculated using the straight-line method over the estimated useful lives of the assets as follows:


Asset category						Estimated useful life
Laboratory equipment						5 years
Computer equipment						3 years
Office equipment, furniture and fixtures						5 years
Leasehold improvements						Lesser of useful life or remaining lease term

Leases

Impairment of long-lived assets

Commitments and contingencies

Revenue recognition

Upfront license fees

Customer options

Research and development services

Milestone payments

For further discussion of accounting for collaboration revenues, see Note 8. Collaboration and license agreements.

Research and development expenses

Stock-based compensation

•The Company estimates the expected term using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the contractual term of the option.

•The risk-free interest rates for periods within the expected life of the option were based on the U.S. Treasury yield curve in effect during the period the options were granted.

•The expected dividend yield is assumed to be zero as the Company has never paid dividends and currently has no plans to pay any dividends on its common stock.

•The fair value of the common stock underlying shared based awards is the quoted market price of the Company’s common stock on the date of the grant.

•The Company recognizes forfeitures as they occur.

Income taxes

Comprehensive loss

Net loss per share

Going concern

Recently issued accounting standards

Defined contribution plan	12 Months Ended
Defined contribution plan	Dec. 31, 2023
Retirement Benefits [Abstract]
Defined contribution plan	Defined contribution plan The Company has a 401(k) retirement plan, the 401(k) Plan, whereby all employees may contribute up to 90% of their eligible compensation, up to the maximum allowable amount set by the Internal Revenue Service. The Company matches 100% of contributions to the 401(k) Plan up to 3%, and matches an additional 50% of contributions up to 5%, for a total potential match of 4% for each employee. During each of the years ended December 31, 2023 and 2022, the Company contributed approximately $1.1 million and $1.0 million, respectively, to the 401(k) Plan.

Property and equipment - Summary of depreciation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1,578	$ 1,676

Leases - Summary of lease term and incremental borrowing rate (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Remaining lease term	8 years 1 month 6 days	9 years 1 month 6 days
Incremental borrowing rate	5.30%	5.30%

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows used in operating activities:
Net loss	$ (132,493)	$ (128,175)
Adjustments to reconcile net loss to cash used in operating activities:
Stock-based compensation expense	27,235	30,016
Depreciation and amortization	1,880	1,676
Reduction in carrying amount of right-of-use asset	6,159	5,896
Accretion of (premium) discount on marketable securities	(3,784)	714
Amortization of debt discount—related party	405	713
Loss on early extinguishment of debt	621	0
Other	77	0
Changes in operating assets and liabilities:
Accounts receivable	(10,327)	4,244
Prepaid expenses and other current and long-term assets	2,723	388
Accounts payable	273	(3,333)
Accrued expenses and other current liabilities	1,316	5,083
Operating lease liability	(4,695)	(507)
Deferred revenue	3,772	(22,654)
Net cash used in operating activities	(106,838)	(105,939)
Cash flows provided by investing activities:
Proceeds from maturities of marketable securities	289,955	283,445
Purchase of marketable securities	(129,898)	(219,527)
Purchases of property and equipment	(1,708)	(5,496)
Net cash provided by investing activities	158,349	58,422
Cash flows provided by financing activities:
Proceeds from issuance of common stock pursuant to the at-the-market equity program, net	57,673	0
Payment of long-term debt − related party	(12,500)	0
Proceeds from exercises of stock options	58	777
Payments for repurchase of common stock for tax withholding	(110)	0
Other	368	370
Net cash provided by financing activities	45,489	1,147
Net change in cash, cash equivalents and restricted cash	97,000	(46,370)
Cash, cash equivalents and restricted cash at beginning of period	33,033	79,403
Cash, cash equivalents and restricted cash at end of period	130,033	33,033
Reconciliation of cash, cash equivalents and restricted cash:
Cash, cash equivalents and restricted cash at end of year	130,033	33,033
Less: restricted cash	(3,443)	(3,279)
Cash and cash equivalents at end of the year	126,590	29,754
Supplemental disclosure of cash flow information:
Deferred revenue in accounts receivable	10,000	0
Cash paid for interest - related party	990	1,624
Cash paid for income taxes	1,003	0
Supplemental disclosures of non-cash investing and financing activities:
Capital expenditures in accounts payable and accrued expenses	18	473
Operating lease liabilities arising from obtaining right-of-use assets	$ 0	$ 44,067

Collaboration and license agreements (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Allocation of total transaction price and unsatisfied transaction price


	Transaction Price Allocated		Transaction Price Unsatisfied
Performance obligations:
Research and development targets	$	61,149	$	17,394
Option rights	6,757		1,670
Total	$	67,906	$	19,064

Schedule of revenue from collaboration agreements

Revenue from collaboration agreements was as follows (in thousands):


	Years Ended December 31,
	2023		2022
Revenue from collaboration agreements:
Roche Agreement	$	9,063	$	4,939
Biogen Agreement	10,623		19,214
Calico Agreement	1,070		6,943
Betta Agreement	—		—
Total revenue from collaboration agreements	$	20,756	$	31,096

Schedule of financial information related to collaboration and license agreements

Supplemental information related to the collaboration and license agreements consisted of the following in the Company’s consolidated balance sheet as of December 31, 2023 (in thousands):


	Accounts Receivable		Deferred Revenue, Current		Deferred Revenue, Net of Current		Deferred Revenue, Total
Supplemental information:
Roche Agreement	$	—	$	2,667	$	11,814	$	14,481
Betta Agreement	1,799		4,000		8,000		12,000
Merck Agreement	10,000		8,000		2,000		10,000
Biogen Agreement	—		804		—		804

Total	$	11,799	$	15,471	$	21,814	$	37,285

Supplemental information related to the collaboration and license agreements consisted of the following in the Company’s consolidated balance sheet as of December 31, 2022 (in thousands):


	Accounts Receivable		Deferred Revenue, Current		Deferred Revenue, Net of Current		Deferred Revenue, Total
Supplemental information:
Roche Agreement	$	417	$	4,649	$	16,895	$	21,544
Biogen Agreement	—		11,427		—		11,427
Calico Agreement	1,056		542		—		542
Total	$	1,473	$	16,618	$	16,895	$	33,513

Schedule of supplemental financial information related to collaboration and license agreements

Supplemental financial information related to the collaboration and license agreements are (in thousands):


	Years Ended December 31,
	2023		2022
Revenue recognized that was included in the contract liability at the beginning of the period	$	20,185	$	25,412
Revenue recognized from performance obligations fully or partially satisfied in previous periods	43		518

Stock-based compensation - Summary of stock option activity - other information (Details) - 2020 Stock Option and Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value of options granted (in dollars per share)	$ 2.84	$ 13.44
Intrinsic value of options exercised (in thousands)	$ 22	$ 1,796

- 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/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (a)(3)
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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://www.xbrl.org/2003/role/disclosureRef
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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 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: 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
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 24: http://www.xbrl.org/2003/role/disclosureRef
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Reference 25: http://www.xbrl.org/2003/role/disclosureRef
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Reference 26: http://www.xbrl.org/2003/role/disclosureRef
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Reference 27: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Stock-based compensation - Narrative (Details) $ in Millions			1 Months Ended		12 Months Ended
	Jan. 01, 2021 shares	Dec. 28, 2015 shares	Jul. 31, 2023 shares	Sep. 30, 2020 period shares	Dec. 31, 2023 USD ($) shares	Jan. 01, 2024 shares	Feb. 28, 2023 shares	Jan. 31, 2023 shares	Dec. 31, 2022 shares	Feb. 28, 2022 shares	Jan. 31, 2022 shares	Jan. 01, 2022 shares	Oct. 31, 2020 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized					150,000,000				150,000,000				150,000,000
Common stock, shares outstanding					60,467,188				48,966,216
Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs \| $					$ 3.1
Expected to be recognized over a weighted average period					1 year 2 months 12 days
Stock-based compensation, shares authorized for issuance										563,500	563,500
Share-based compensation, number of common stock issuable per RSU vested					1
Time-Based Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs \| $					$ 3.5
Expected to be recognized over a weighted average period					3 years 2 months 12 days
Stock-based compensation, shares authorized for issuance							824,600	824,600
Share-based compensation, number of common stock issuable per RSU vested					1
Employee Stock Option \| Share-Based Payment Arrangement, Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation, shares authorized for issuance			351,000
Stock-based compensation, options vesting description			four years
Options outstanding (in shares)					351,000
Employee Stock Option \| Share-Based Payment Arrangement, Employee \| Share-Based Payment Arrangement, Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation, options vesting description			one year
Employee Stock Option \| Share-Based Payment Arrangement, Employee \| Share-Based Payment Arrangement, Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation, options vesting description			P3M
2015 Incentive Stock Option and Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance		2,525,327
Cliff vesting period		1 year
Contractual life of options from the date of grant		10 years
Common stock shares available for issuance					3,358,336
2015 Incentive Stock Option and Grant Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period		5 years
2015 Incentive Stock Option and Grant Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period		8 years
2020 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance				6,567,144
Common stock shares available for issuance					3,358,336
Percentage of outstanding shares of common stock	5.00%
Unrecognized compensation costs \| $					$ 51.6
Expected to be recognized over a weighted average period					2 years 1 month 6 days
Options outstanding (in shares)					9,475,009				6,993,052
2020 Stock Option and Incentive Plan \| Subsequent event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized						3,023,359
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance					1,673,129
Percentage of outstanding shares of common stock	1.00%
Common stock, shares authorized												604,671
Maximum authorized payroll deduction percentage of eligible compensation for eligible employees				15.00%
Number of annual offering periods (or more) \| period				1
Shares issued under employee stock purchase plan (in shares)					133,784
Common stock, shares outstanding	656,714

Net loss per share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net loss per share

As described in Note 2, Summary of significant accounting policies, for periods in which the Company reports a net loss, potentially dilutive securities have been excluded from the computation of diluted net loss per share as their effects would be anti-dilutive. 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 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
Options to purchase common stock	9,475,009	6,993,052

Basic and diluted loss per share is computed by dividing net loss by the weighted-average common shares outstanding (in thousands, except share and per share data):


	Years Ended December 31,
	2023		2022
Numerator:


Net loss —basic and diluted	$	(132,493)	$	(128,175)
Denominator:
Weighted-average common stock outstanding—basic and diluted	49,640,505		48,861,665
Net loss per share —basic and diluted	$	(2.67)	$	(2.62)

Stockholder's equity (Details)	1 Months Ended		12 Months Ended		26 Months Ended
Stockholder's equity (Details)	Jan. 31, 2024 USD ($) shares	Nov. 30, 2021 USD ($)	Dec. 31, 2023 USD ($) vote $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Oct. 31, 2020 $ / shares shares
Subsidiary, Sale of Stock [Line Items]
Preferred stock, shares authorized \| shares			10,000,000	10,000,000	10,000,000	10,000,000
Common stock, shares authorized \| shares			150,000,000	150,000,000	150,000,000	150,000,000
Preferred stock, par value (in dollars per share) \| $ / shares			$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, par value (in dollars per share) \| $ / shares			$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, number of votes per share \| vote			1
Issuance and sale of common stock \| $			$ 57,673,000
At-the-market offerings \| Equity Distribution Agreement with Cowen and Company, LLC
Subsidiary, Sale of Stock [Line Items]
Issuance and sale of common stock \| $			$ 57,700,000	$ 0	$ 71,800,000
Issuance of common stock pursuant to the at-the-market equity program, net (in shares) \| shares			11,186,142		13,686,743
Price per share (in dollars per share) \| $ / shares			$ 5.42		$ 5.42
At-the-market offerings \| Equity Distribution Agreement with Cowen and Company, LLC \| Subsequent event
Subsidiary, Sale of Stock [Line Items]
Issuance and sale of common stock \| $	$ 14,100,000
Issuance of common stock pursuant to the at-the-market equity program, net (in shares) \| shares	2,500,601
Maximum \| At-the-market offerings \| Equity Distribution Agreement with Cowen and Company, LLC
Subsidiary, Sale of Stock [Line Items]
Issuance and sale of common stock \| $		$ 200,000,000

Summary of significant accounting policies- Summary of property and equipment - useful lives (Details)	Dec. 31, 2023
Laboratory equipment
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Computer equipment
Property Plant And Equipment [Line Items]
Estimated useful life	3 years
Office equipment, furniture and fixtures
Property Plant And Equipment [Line Items]
Estimated useful life	5 years

Stock-based compensation - Summary of significant valuation assumptions (Details) - 2020 Stock Option and Incentive Plan	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	3.45%	1.47%
Risk-free interest rate, maximum	4.73%	4.22%
Expected volatility, minimum	81.99%	81.36%
Expected volatility, maximum	86.15%	88.75%
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected option life (years)	5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected option life (years)	6 years 1 month 9 days	6 years 1 month 9 days

Income taxes - Narrative (Details) - USD ($)	12 Months Ended
Income taxes - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Income Tax [Line Items]
Deferred tax assets, valuation allowance	$ 145,589,000	$ 110,120,000
Net valuation allowance increases	35,500,000	34,700,000
Federal net operating loss carryforwards	214,900,000	171,600,000
Federal net operating loss carryforwards do not expire	$ 214,900,000
Percentage of taxable income limitation under TCJA	80.00%
State net operating loss carryforwards	$ 315,300,000	273,600,000
Accrued interest or penalties related to uncertain tax benefits	0	0
IRS
Income Tax [Line Items]
Net operating loss carryforwards limited and expire due to ownership changes	0
Federal \| Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	12,600,000	9,100,000
State \| Research tax credit carryforward
Income Tax [Line Items]
Tax credit carryforwards	$ 5,200,000	$ 2,900,000

Nature of the business (Details) - USD ($) $ in Thousands	12 Months Ended
Nature of the business (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ (132,493)	$ (128,175)
Accumulated deficit	528,383	$ 395,890
Cash, cash equivalents and marketable securities	$ 281,700

- Definition

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

+ References

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Defined contribution plan (Details) - USD ($) $ in Millions	12 Months Ended
Defined contribution plan (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Contribution Plan Disclosure [Line Items]
Pre-tax compensation of employees	90.00%
Percentage of employer discretion contribution	100.00%
Defined contribution plan, employer matching contribution, percent of match	3.00%
Defined contribution plan, employer matching contribution, additional percent of employees' gross pay	50.00%
Defined contribution plan, employer matching contribution, additional percent of match	5.00%
Employer discretionary contribution amount	$ 1.1	$ 1.0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	4.00%

Collaboration and license agreements - Schedule of financial information related to collaboration and license agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable	$ 11,799	$ 1,473
Deferred revenue, current	15,471	16,618
Deferred revenue, net of current	21,814	16,895
Deferred Revenue, Total	37,285	33,513
Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable	0	417
Deferred revenue, current	2,667	4,649
Deferred revenue, net of current	11,814	16,895
Deferred Revenue, Total	14,481	21,544
Betta Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable	1,799
Deferred revenue, current	4,000
Deferred revenue, net of current	8,000
Deferred Revenue, Total	12,000
Merck Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable	10,000
Deferred revenue, current	8,000
Deferred revenue, net of current	2,000
Deferred Revenue, Total	10,000
Biogen Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable	0	0
Deferred revenue, current	804	11,427
Deferred revenue, net of current	0	0
Deferred Revenue, Total	$ 804	11,427
Calico Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts Receivable		1,056
Deferred revenue, current		542
Deferred revenue, net of current		0
Deferred Revenue, Total		$ 542

Income taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of income tax (benefit) expense

Income tax (benefit) expense consists of the following (in thousands):


	Years Ended December 31,
	2023		2022
Current tax provision:
Current federal provision	$	—	$	—
Current state provision	76		—
Current foreign provision	1,204		—
Total current provision	1,280		—
Deferred tax provision:
Deferred federal provision	—		—
Deferred state provision	—		—
Deferred foreign provision	—		—
Total tax provision	$	1,280	$	—

Schedule of effective income tax rate reconciliation

A reconciliation of the expected income tax (benefit) expense computed at the statutory federal rate to income taxes as reflected in the consolidated financial statements was as follows:


	Years Ended December 31,
	2023		2022
Income tax benefit computed at federal statutory tax rate	21.0	%	21.0	%
State tax—net of federal	4.2	%	8.0	%
Federal credits	3.5	%	1.4	%
State credits	1.4	%	0.1	%
Other permanent differences	(0.2)	%	(0.8)	%
Withholding tax	(0.9)	%	—	%
Stock-based compensation	(2.8)	%	(3.0)	%


Valuation allowance	(27.2)	%	(26.7)	%
Total	(1.0)	%	—	%

Schedule of deferred tax assets and liabilities

credit carryforwards. Significant components of the Company’s deferred tax assets and deferred tax liabilities were as follows (in thousands):


	As of December 31,
	2023		2022
Deferred tax assets:
Net operating losses	$	61,036	$	54,300
Capitalized research and experimental expenditures	51,401		27,568
Operating lease liability	20,611		21,443
R&D and investment tax credits	18,049		11,519
Stock-based compensation	9,061		6,296
Deferred revenue	3,881		8,457
Foreign tax credit	1,204		—
Capitalized start-up costs	555		699
Unrealized gain/loss	—		1,090
Other	27		354
Total gross deferred tax assets	165,825		131,726
Deferred tax liabilities:
Right-of-use asset	(18,573)		(19,868)
Fixed assets	(1,663)		(1,738)

Less: valuation allowance	(145,589)		(110,120)
Net deferred taxes	$	—	$	—

Leases - Narrative (Details) $ in Thousands	1 Months Ended
Leases - Narrative (Details) $ in Thousands	Jan. 31, 2022 USD ($) period contract	Jul. 31, 2017 period	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Apr. 30, 2018 USD ($)
Lessee Lease Description [Line Items]
Liabilities under lease			$ 70,976
Right-of-use assets			63,956	$ 70,116
Watertown Lease
Lessee Lease Description [Line Items]
Liabilities under lease	$ 44,100
Right-of-use assets	$ 44,400
Watertown Lease \| Office and Laboratory Space
Lessee Lease Description [Line Items]
Lease contract term		10 years
Number of extensions \| period		1
Lease extension term		5 years			5 years
Liabilities under lease					$ 15,100
Right-of-use assets					16,700
Construction costs					$ 1,500
Watertown Lease \| Newly Leased Space
Lessee Lease Description [Line Items]
Number of extensions \| period	1
Lease extension term	5 years
Liabilities under lease	$ 20,100
Right-of-use assets	$ 20,100
Lease term	10 years
Tenant improvements	$ 2,600
Restricted cash			$ 3,300	$ 3,300
Number of amended lease separate contracts \| contract	2