v3.26.1
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Feb. 28, 2026
Jun. 30, 2025
Document and Entity Information      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Document Transition Report false    
Entity File Number 001-42270    
Entity Registrant Name Zenas BioPharma, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 93-2749244    
Entity Address, Address Line One 852 Winter Street    
Entity Address, Adress Line Two Suite 250    
Entity Address, City or Town Waltham    
Entity Address State Or Province MA    
Entity Address, Postal Zip Code 02451    
City Area Code 857    
Local Phone Number 271-2954    
Entity Well-known Seasoned Issuer Yes    
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 true    
Entity Ex Transition Period false    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Title of 12(b) Security Common stock, par value $0.0001 per share    
Trading Symbol ZBIO    
Security Exchange Name NASDAQ    
Entity Public Float     $ 259.3
Entity Common Stock, Shares Outstanding   57,361,260  
Documents Incorporated by Reference [Text Block]

Portions of the Registrant’s definitive proxy statement relating to the 2026 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after 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.

   
Auditor Name Ernst & Young LLP    
Auditor Location Boston, Massachusetts    
Auditor Firm ID 42    
Entity Central Index Key 0001953926    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Amendment Flag false