v3.26.1
Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2026
May 06, 2026
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Entity Central Index Key 0001835597  
Entity Registrant Name PEPGEN INC.  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   69,169,215
Entity Shell Company false  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Title of 12(b) Security Common stock, par value $0.0001 per share  
Trading Symbol PEPG  
Security Exchange Name NASDAQ  
Entity File Number 001-41374  
Entity Tax Identification Number 85-3819886  
Entity Incorporation, State or Country Code DE  
Entity Address, Address Line One 321 Harrison Ave. 8th Floor  
Entity Address, City or Town Boston  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02118  
City Area Code 781  
Local Phone Number 797-0979  
Document Quarterly Report true  
Document Transition Report false