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Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Feb. 23, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Document Transition Report false    
Entity File Number 001-39567    
Entity Registrant Name C4 Therapeutics, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 47-5617627    
Entity Address, Address Line One 490 Arsenal Way    
Entity Address, Address Line Two Suite 120    
Entity Address, City or Town Watertown    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 02472    
City Area Code 617    
Local Phone Number 231-0700    
Title of 12(b) Security Common Stock, $0.0001 par value per share    
Trading Symbol CCCC    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 100,051,846
Entity Common Stock, Shares Outstanding   97,578,175  
Amendment Flag false    
Entity Central Index Key 0001662579    
Documents Incorporated by Reference
DOCUMENTS INCORPORATED BY REFERENCE
Portions of the registrant’s definitive proxy statement for its 2026 Annual Meeting of Stockholders to be filed pursuant to Regulation 14A within 120 days of the end of the registrant’s fiscal year ended December 31, 2025 are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.