| December 31, | ||||||||
| 2023 | 2022 | |||||||
| Assets | ||||||||
| Current assets: | ||||||||
| Cash and cash equivalents | $ | 405,732 | $ | 1,872 | ||||
| Prepaid expenses and other current assets | 3,745 | 2,055 | ||||||
| Total current assets | 409,477 | 3,927 | ||||||
| Operating lease right-of-use assets | 28,222 | 2,165 | ||||||
| Restricted cash | 567 | — | ||||||
| Property and equipment, net | 10,379 | 3,368 | ||||||
| Other non-current assets | 4,391 | 783 | ||||||
| Total assets | $ | 453,036 | $ | 10,243 | ||||
| Liabilities, Convertible Preferred Stock and Stockholders’ Equity (Deficit) | ||||||||
| Current liabilities: | ||||||||
| Accounts payable | $ | 5,013 | $ | 3,483 | ||||
| Accrued clinical and research and development expenses | 7,242 | 1,646 | ||||||
| Accrued expenses and other current liabilities | 6,629 | 3,391 | ||||||
| Operating lease liabilities, current | 2,278 | 1,006 | ||||||
| Convertible notes–related party | — | 11,635 | ||||||
| Convertible notes | — | 9,619 | ||||||
| Derivative liabilities | — | 12,705 | ||||||
| Financial commitment liabilities–related party | — | 412 | ||||||
| Financial commitment liabilities | — | 240 | ||||||
| Total current liabilities | 21,162 | 44,137 | ||||||
| Operating lease liabilities, non-current | 26,263 | 1,092 | ||||||
| Other non-current liabilities | 225 | 250 | ||||||
| Total liabilities | 47,650 | 45,479 | ||||||
| Commitments and contingencies (Note 13) | ||||||||
| Stockholders’ equity (deficit): | ||||||||
| Convertible preferred stock, $0.001 par value; 11,000,000 shares authorized and 810,700 issued and outstanding at December 31, 2022 (aggregate liquidation preference of $11,000 at December 31, 2022) | — | 1 | ||||||
| Common stock, $0.001 par value; 500,000,000 and 29,000,000 shares authorized at December 31, 2023 and 2022, respectively; 41,205,551 and 1,091,800 shares issued and outstanding at December 31, 2023 and 2022, respectively | 41 | 1 | ||||||
| Additional paid-in capital | 550,491 | 11,761 | ||||||
| Accumulated deficit | (145,146) | (46,999) | ||||||
| Total stockholders’ equity (deficit) | 405,386 | (35,236) | ||||||
| Total liabilities, convertible preferred stock and stockholders’ equity (deficit) | $ | 453,036 | $ | 10,243 | ||||
| Year ended December 31, | ||||||||
| 2023 | 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 | ||||
