Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (381,641)	$ (64,772)	$ (41,839)
Adjustments to reconcile net loss to net cash used in operations:
Stock-based compensation expense	47,318	4,052	233
Expense related to acquired in-process research and development assets	133,057	0	25,000
Net amortization of premiums and accretion of discounts on short-term marketable securities	(10,495)	(246)	0
Change in fair value of derivative tranche liability	(10,291)	(487)	0
Depreciation and amortization expense	115	0	0
Non-cash lease expense	153	0	0
Changes in assets and liabilities:
Prepaid expense and other current assets	(11,313)	(941)	(49)
Prepaid expenses and other assets, non-current	1,528	(1,964)	0
Accounts payable	34,443	3,776	1,119
Accrued research and development expenses	24,914	(3,980)	9,697
Accrued compensation and other current liabilities	1,691	3,042	860
Operating lease liability	(154)	0	0
Severance liability	970	0	0
Net cash used in operating activities	(169,705)	(61,520)	(4,979)
Cash flows from investing activities
ValenzaBio assets acquisition cash acquired, net of acquisition costs	10,007	0	0
Cash paid to acquire in-process research and development assets	(10,000)	0	(25,000)
Purchase of marketable securities	(956,512)	(175,970)	0
Proceeds from maturities of short-term marketable securities	373,359	128,179	0
Sales of marketable securities	137,696	0	0
Purchase of property, plant and equipment	(2,294)	0	0
Payments for ValenzaBio Acquisition costs	0	(83)	0
Net cash used in investing activities	(447,744)	(47,874)	(25,000)
Cash flows from financing activities
Issuance of common stock upon initial public offering, net of commissions and issuance costs	574,134	0	0
Proceeds from exercise of common stock options and issuance of common stock under the employee stock purchase plan	2,627	0	16
Proceeds from the issuance of redeemable convertible preferred stock, net of issuance costs	0	263,973	124,704
Proceeds allocated to the derivative tranche liability		10,778	0
Payments for deferred offering costs	0	(489)	0
Taxes paid related to net share settlement of restricted stock units	(8,325)	0	0
Net cash provided by financing activities	568,436	274,262	124,720
Net increase (decrease) in cash and cash equivalents	(49,013)	164,868	94,741
Cash and cash equivalents, at beginning of year	267,110	102,242	7,501
Cash and cash equivalents, at end of year	218,097	267,110	102,242
Supplemental disclosure of cash flow information:
Conversion of 40,743,522 redeemable convertible preferred stock upon the closing of initial public offering	396,593	0	0
Common stock issued in connection with ValenzaBio acquisition	128,735	0	0
Right-of-use assets obtained in exchange for operating lease liability	1,348	0	0
Deferred offering costs included in accrued compensation and other current liabilities and accounts payable	0	285	0
ValenzaBio Acquisition costs included in accounts payable	$ 0	$ 1,038	$ 0