v3.26.1
Cover
Mar. 26, 2026
Cover [Abstract]  
Document Type 8-K
Document Period End Date Mar. 26, 2026
Entity Registrant Name GOLUB CAPITAL PRIVATE INCOME FUND S
Entity Incorporation, State or Country Code DE
Securities Act File Number 814-01945
Entity Tax Identification Number 39-3613464
Entity Address, Address Line One 200 Park Avenue
Entity Address, Address Line Two 25th Floor
Entity Address, City or Town New York
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10166
City Area Code 212
Local Phone Number 750-6060
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Emerging Growth Company true
Amendment Flag false
Entity Central Index Key 0002082557
Entity Ex Transition Period false