v3.26.1
Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2026
Aug. 06, 2026
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Entity Registrant Name Cogent Biosciences, Inc.  
Entity Central Index Key 0001622229  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   173,524,982
Entity Shell Company false  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity File Number 001-38443  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 46-5308248  
Entity Address, Address Line One 180 Third Avenue  
Entity Address, Address Line Two 4th Floor  
Entity Address, City or Town Waltham  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02451  
City Area Code (617)  
Local Phone Number 945-5576  
Title of 12(b) Security Common Stock, $0.001 Par Value  
Trading Symbol COGT  
Security Exchange Name NASDAQ  
Former Address [Member]    
Document Information [Line Items]    
Entity Address, Address Line One 275 Wyman Street  
Entity Address, Address Line Two 3rd Floor  
Entity Address, City or Town Waltham  
Entity Address, State or Province MA