BASIS OF PRESENTATION AND ACCOUNTING POLICIES - Narrative (Details) - USD ($)		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Nov. 05, 2025	Sep. 26, 2025
Temporary Equity [Line Items]
Deferred offering costs			$ 0		$ 10,680,000
Loss on issuance of convertible preferred stock		$ 379,619,000	0	$ 0
Warrants issued to purchase common stock (in shares)						2,552,467
Aggregate grant date fair value, warrants						$ 67,236,000
Research and development	[1]	$ 259,892,000	$ 206,910,000	$ 138,273,000
Product Concentration Risk | Revenue | Transferred over Time
Temporary Equity [Line Items]
Concentration risk, percentage		44.00%	49.00%	38.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-10-01
Temporary Equity [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Temporary Equity [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period		12 months
Related Party
Temporary Equity [Line Items]
Research and development		$ 6,073,000	$ 0	$ 0
Fair Value, Inputs, Level 1
Temporary Equity [Line Items]
Cash equivalents, fair value		1,550,925,000	$ 190,223,000
GE Aerospace
Temporary Equity [Line Items]
Exercise price, warrants (in dollars per share)						$ 0.002
GE Aerospace | Related Party
Temporary Equity [Line Items]
Loss on issuance of convertible preferred stock		215,585,000
Warrants issued to purchase common stock (in shares)						2,552,467
GE Collaboration Agreement
Temporary Equity [Line Items]
Unrecognized compensation cost		61,163,000
GE Collaboration Agreement | Related Party
Temporary Equity [Line Items]
Research and development		6,335,000
Warrant expense		$ 6,073,000
Series C and Series C-1
Temporary Equity [Line Items]
Convertible preferred stock, purchase price (in dollars per share)		$ 17.94
Minimum | Series C and Series C-1
Temporary Equity [Line Items]
Convertible preferred stock, fair value range (in dollars per share)		17.94
Maximum | Series C and Series C-1
Temporary Equity [Line Items]
Convertible preferred stock, fair value range (in dollars per share)		$ 30.83

[1] Includes related party amounts of $6,073, $0 and $0 (research and development) and $1,084, $(2,899) and $(1,441) (general and administrative) as of December 31, 2025, 2024 and 2023, respectively (see Note 14)