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Cover - shares
 9 Months Ended
Sep. 30, 2025
Nov. 03, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2025  
Document Transition Report false  
Entity File Number 001-36177  
Registrant Name Crescent Biopharma, Inc.  
Entity Incorporation, State or Country Code E9  
Entity Tax Identification Number 06-1686563  
Entity Address, Address Line One 300 Fifth Avenue  
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 430-5595  
Title of 12(b) Security Ordinary Shares, $0.001 par value per share  
Trading Symbol CBIO  
Security Exchange Name NASDAQ  
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  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   13,892,516
Entity Central Index Key 0001253689  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Document Fiscal Year Focus 2025