Segment Reporting - Summary of Segment Loss Including Significant Segment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2025	Jun. 30, 2024
Research and development expenses:
Segment Loss and Net loss	$ 42,081	$ 44,635	$ 28,803	$ 26,693	$ 86,716	$ 55,496
Operating Segment
Research and development expenses:
Other research and development expenses	12,289		13,483		27,090	22,334
General and administrative expenses	8,594		6,114		18,569	12,996
Interest (income)	(2,364)		(4,694)		(5,189)	(7,429)
Interest expense and other expenses, net	35		62		87	132
Segment Loss and Net loss	42,081		28,803		86,716	55,496
Operating Segment | KYV-101 program
Research and development expenses:
External research and development expenses allocated by program	22,541		13,326		44,661	24,323
Operating Segment | Other Programs
Research and development expenses:
External research and development expenses allocated by program	$ 986		$ 512		$ 1,498	$ 3,140