CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Operating expenses:
Research and development	$ 187,402	$ 142,903
General and administrative expense	54,246	54,016
Total operating expenses	241,648	196,919
Loss from operations	(241,648)	(196,919)
Other income (expense):
Interest income	22,212	29,660
Other income (expense), net	(443)	(199)
Net loss before income taxes	(219,879)	(167,458)
Effective tax rate	0	117
Net loss	(219,879)	(167,575)
Net loss attributable to noncontrolling interests	(0)	(192)
Net loss attributable to Cullinan	(219,879)	(167,383)
Comprehensive income (loss):
Net loss	(219,879)	(167,575)
Unrealized gain (loss) on investments	1,153	(4)
Comprehensive loss	(218,726)	(167,579)
Comprehensive loss attributable to noncontrolling interests	(0)	(192)
Comprehensive loss attributable to Cullinan	(218,726)	(167,387)
Common Stock
Other income (expense):
Net loss attributable to Cullinan	$ (198,212)	$ (149,393)
Basic and diluted net loss per share attributable to Cullinan:
Basic	$ (3.36)	$ (2.78)
Diluted	$ (3.36)	$ (2.78)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Basic	59,050	53,771
Diluted	59,050	53,771
Preferred Stock
Other income (expense):
Net loss attributable to Cullinan	$ (21,667)	$ (17,990)
Basic and diluted net loss per share attributable to Cullinan:
Basic	$ (33.57)	$ (27.78)
Diluted	$ (33.57)	$ (27.78)
Weighted-average shares used in computing basic and diluted net loss per share attributable to Cullinan:
Basic	645	648
Diluted	645	648