Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
OPERATING ACTIVITIES
Net loss	$ (98,147)	$ (40,951)
Adjustments to reconcile net loss to net cash used in operating activities:
Net change in fair value of redeemable convertible preferred stock tranche obligations	8,783
Stock-based compensation expense	3,327	297
Loss on extinguishment of convertible notes	2,316
Amortization of operating lease right-of-use assets	2,201	1,040
Noncash interest expense	1,604	4,942
Depreciation	1,491	404
Acquired in-process research and development	1,505	1,013
Change in fair value of derivative liabilities	(6,453)	1,216
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,590)	(1,912)
Other non-current assets	(3,608)	(267)
Accounts payable	757	2,819
Accrued clinical and research and development expenses	4,673	1,222
Accrued expenses and other current liabilities	3,792	2,175
Operating lease liabilities	(1,815)	(1,070)
Net cash used in operating activities	(81,164)	(29,072)
INVESTING ACTIVITIES
Purchase of property and equipment	(8,277)	(2,724)
Purchase of in-process research and development	(715)	(558)
Net cash used in investing activities	(8,992)	(3,282)
FINANCING ACTIVITIES
Proceeds from issuance of common stock on initial public offering, net of commissions	296,607
Proceeds from issuance of redeemable convertible preferred stock and tranche obligations, net of issuance costs	199,918
Proceeds from issuance of convertible notes, net of issuance costs - related party	2,212	15,948
Proceeds from issuance of convertible notes, net of issuance costs	1,286	12,505
Proceeds from issuance of convertible preferred stock and tranche commitment, net of issuance costs		5,500
Proceeds from issuance of restricted stock awards		232
Proceeds from exercise of stock options	34
Payment of deferred initial public offering costs	(5,474)
Net cash provided by financing activities	494,583	34,185
Net increase in cash, cash equivalents and restricted cash	404,427	1,831
Cash and cash equivalents at beginning of period	1,872	41
Cash, cash equivalents, and restricted cash at end of period	406,299	1,872
COMPONENTS OF CASH, CASH EQUIVALENTS, AND RESTRICTED CASH
Cash and cash equivalents	405,732	1,872
Restricted cash	567
Total cash, cash equivalents, and restricted cash	406,299	1,872
SUPPLEMENTAL NON-CASH INVESTING AND FINANCING ACTIVITIES
Reclassification of shares of Series Seed redeemable convertible preferred stock to mezzanine equity	9,830
Conversion of convertible notes to shares of Series A-2 redeemable convertible preferred stock	35,576
Reclassification of tranche obligation asset to Series A-1 redeemable convertible preferred stock	1,910
Reclassification of tranche obligation liability to Series A-1 redeemable convertible preferred stock	18,010
Conversion of redeemable convertible preferred stock into common stock on completion of initial public offering	254,107
Purchase of property and equipment in accounts payable and accrued expenses and other current liabilities	883	623
In-process research and development costs in accounts payable, accrued expenses and other current liabilities, and other non-current liabilities	1,273	383
Issuance of shares in exchange for in-process research and development		72
Deferred offering costs related to initial public offering included in accounts payable and accrued expenses and other current liabilities	$ 105
Deferred issuance costs for second tranche of Series A-1 redeemable convertible preferred stock in accounts payable and accrued expenses and other current liabilities		$ 74