Income taxes

12 Months Ended

Dec. 31, 2024

Income Tax Disclosure [Abstract]

Income taxes

Income taxes

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

	Years Ended December 31,
	2024		2023
Current tax provision:
Current federal provision	$	—	$	—
Current state provision	131		76
Current foreign provision	—		1,204
Total current provision	131		1,280
Deferred tax provision:
Deferred federal provision	—		—
Deferred state provision	—		—
Deferred foreign provision	—		—
Total tax provision	$	131	$	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,
	2024		2023
Income tax benefit computed at federal statutory tax rate	21.0	%	21.0	%
State tax—net of federal	6.4	%	4.2	%
Federal credits	3.0	%	3.5	%
State credits	1.3	%	1.4	%
Other permanent differences	(1.0)	%	(0.2)	%
Withholding tax	—	%	(0.9)	%
Stock-based compensation	(4.2)	%	(2.8)	%
Valuation allowance	(26.6)	%	(27.2)	%
Total	(0.1)	%	(1.0)	%

The Company's effective tax rate as of December 31, 2024, was driven by income taxes related to the C4T Securities Corporation, a Massachusetts security corporation. This resulted in a tax provision of $0.1 million and effective tax rate of (0.1)%.

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,
	2024		2023
Deferred tax assets:
Net operating losses	$	62,429	$	61,036
Capitalized research and experimental expenditures	68,370		51,401
Operating lease liability	19,083		20,611
R&D and investment tax credits	23,646		18,049
Stock-based compensation	11,003		9,061
Deferred revenue	6,671		3,881
Foreign tax credit	—		1,204
Capitalized start-up costs	392		555
Other	25		27
Total gross deferred tax assets	191,619		165,825
Deferred tax liabilities:
Right-of-use asset	(16,697)		(18,573)
Fixed assets	(1,382)		(1,663)
Less: valuation allowance	(173,540)		(145,589)
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, 2024 and 2023, 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, 2024 and 2023. The valuation allowance for deferred tax assets as of December 31, 2024 and 2023 was $173.5 million and $145.6 million, respectively. The net valuation allowance increased $28.0 million and $35.5 million during the years ended December 31, 2024 and 2023,

respectively. The change during the year ended December 31, 2024 was primarily due to the increase in net operating loss, or NOL, and tax credits carryforward, capitalization of research and experimental expenditures, and a decrease in deferred revenue recognized during the year and a decrease in right-of-use asset deferred tax liability.

As of December 31, 2024 and 2023, the Company had $222.8 million and $214.9 million gross United States federal net 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 $222.8 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 NOLs arising in 2018, 2019 and 2020 to the five prior tax years. In addition, NOLs 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, 2024 and 2023, the Company has total gross United States state NOL carryforwards of $338.3 million and $315.3 million, respectively, which may be available to offset future taxable income that expire at various dates through 2044.

As of December 31, 2024 and 2023, the Company has United States federal research credit carryforwards of $15.8 million and $12.6 million, respectively, which are available to offset future federal income tax liabilities, which expire at various dates through 2044. As of December 31, 2024 and 2023, the Company has United States state research credit carryforwards of $7.8 million and $5.2 million, respectively, which are available to reduce future tax liabilities which expire at various dates through 2039.

NOL 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 NOL 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 NOL 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, 2024 and 2023, the Company had no accrued interest or penalties related to unrecorded tax benefits.

The Company files income tax returns as prescribed by tax laws of the jurisdictions in which it operates. The federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2021 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.