Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Cash flows from operating activities:
Net loss	$ (212,749)	$ (142,494)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,564	1,837
Amortization of right-of-use asset	415	342
Accretion of discounts on marketable securities	(1,030)	(2,839)
Share-based compensation expense	29,513	17,797
Loss on disposal of property and equipment	80	841
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(11,302)	(3,447)
Accounts payable	1,143	(6,887)
Accrued expenses and other current liabilities	4,073	(1,167)
Deferred revenue	0	(6,941)
Operating lease liabilities	6,212	(8)
Net cash used in operating activities	(181,081)	(142,966)
Cash flows from investing activities:
Purchases of marketable securities	(302,177)	(123,266)
Maturities of marketable securities	54,000	200,000
Purchases of in-process research and development assets	(9,014)	(6,246)
Purchases of property and equipment	(5,667)	(5,686)
Net cash (used in) provided by investing activities	(262,858)	64,802
Cash flows from financing activities:
Proceeds from exercise of stock options	3,663	839
Proceeds from public offerings	0	172,500
Proceeds from issuance of common stock under ATM	0	45,897
Payment of offering costs	(364)	(11,674)
Net cash provided by financing activities	3,299	207,562
Net (decrease) increase in cash and cash equivalents and restricted cash	(440,640)	129,398
Cash and cash equivalents and restricted cash at beginning of period	653,692	143,451	$ 143,451
Cash and cash equivalents and restricted cash at end of period	213,052	272,849	653,692
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents	212,842	272,639	653,482
Restricted cash	210	210	210
Total cash, cash equivalents, and restricted cash	213,052	272,849	$ 653,692
Supplemental disclosures of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for operating lease liabilities	1,318	0
Purchases of in-process research and development assets, including payments owed upon achievement of development milestones, in accounts payable and accrued expenses	986	0
Purchases of property and equipment in accounts payable and accrued expenses and other current liabilities	17	1,248
Remeasurement of operating right-of-use asset and lease liability due to lease modification	$ 0	$ 811