Income Tax - Income tax reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	$ (53,669)	$ (38,247)	$ (17,637)
State and local income taxes, net of federal income tax benefit	(195)	(542)	(147)
Research and development tax credits	(6,308)	(7,801)	(2,151)
Change in valuation allowance	53,013	41,309	17,882
Nontaxable or nondeductible items	4,775	2,738	1,222
Changes in unrecognized tax benefits	2,049	2,551	865
Other adjustments	613	10	(34)
Total Provision	$ 278	$ 18	$ 0
U.S. federal statutory tax rate	(21.00%)	(21.00%)	(21.00%)
State and local income taxes, net of federal income tax benefit	(0.10%)	(0.30%)	(0.20%)
Research and development tax credits	(2.50%)	(4.30%)	(2.60%)
Change in valuation allowance	20.70%	22.70%	21.30%
Nontaxable or nondeductible items	1.90%	1.50%	1.50%
Changes in unrecognized tax benefits	0.80%	1.40%	1.00%
Other adjustments	0.30%	0.00%	0.00%
Effective tax rate	0.10%	0.00%	0.00%