v3.26.1
Description of Business and Basis of Presentation (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 22, 2026
Feb. 05, 2026
Sep. 05, 2025
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Description of Business and Basis of Presentation                    
Cash and cash equivalents       $ 93,016       $ 93,016   $ 23,719
Net loss       (31,009) $ (21,344) $ (3,799) $ (3,137) (52,353) $ (6,936)  
Net cash used in operating activities               (42,462) $ (3,632)  
Accumulated deficit       (119,080)       $ (119,080)   $ (66,727)
Issuance of common stock         $ 80,000          
Placement Agent Warrants                    
Description of Business and Basis of Presentation                    
Warrants to purchase (in shares)     586,666              
Private Placement                    
Description of Business and Basis of Presentation                    
Issuance of common stock (in shares)   5,333,333 10,000,000              
Purchase price (in dollars per share)   $ 15 $ 3              
Issuance of common stock     $ 30,000              
Initial public offering                    
Description of Business and Basis of Presentation                    
Net proceeds from initial public offering $ 34,291     $ 34,291            
Issuance of common stock (in shares) 2,500,000                  
Purchase price (in dollars per share) $ 16                  
Legacy Deep Fission                    
Description of Business and Basis of Presentation                    
Number of shares issued per share (in shares)     17.32141              
Shares issued for services (in shares)     85,000