Organization	9 Months Ended
Jun. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Note 1. Organization Golub Capital Private Income Fund S (“GPIF S” or the “Company”), is a Delaware statutory trust formed on July 22, 2025. The Company is an externally managed, non-diversified, closed-end management investment company that commenced operations on December 31, 2025, the effective date of the Company’s election to be regulated as a business development company (“BDC”) under the Investment Company Act of 1940, as amended (the “1940 Act”). In addition, for U.S. federal income tax purposes, beginning with its tax year ending September 30, 2026, the Company intends to elect to be treated as a regulated investment company (“RIC”) under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). The Company’s fiscal year end is September 30. The Company’s investment objective is to generate current income and capital appreciation by investing primarily in privately originated and privately negotiated investments, predominantly through direct lending to U.S. private companies in the middle-market in the form of one stop (a loan that combines characteristics of traditional first lien senior secured loans and second lien or subordinated loans and that are often referred to by other middle-market lenders as unitranche loans) and other senior secured loans. The Company could selectively invest in second lien and subordinated loans (including loans that rank senior only to a borrower’s equity securities and ranks junior to all of such borrower’s other indebtedness in priority of payment) of private companies. The Company also expects to invest in liquid credit instruments, including secured floating rate syndicated loans (e.g., broadly syndicated loans), securitized products and corporate bonds, and the Company’s portfolio may, but will not necessarily, initially be comprised of a greater percentage of such instruments than it will as the Company’s investment program matures, though the exact allocation could vary from time to time depending on market conditions and available investment opportunities. The Company’s portfolio could also include other credit-related investments, including, without limitation, structured and synthetic debt investments and debt investments accompanied by equity securities, preferred equity and, to a limited extent, common equity investments not associated with a debt investment. The Company has entered into an investment advisory agreement dated December 5, 2025 (the “Investment Advisory Agreement”) with GC Advisors, LLC (the “Investment Adviser”), under which the Investment Adviser manages the day-to-day operations of, and provides investment advisory services to, the Company. Under an administration agreement dated December 5, 2025 (the “Administration Agreement”) the Company is provided with certain services by an administrator, which is currently Golub Capital LLC (the “Administrator”). The Company offers its common shares of beneficial interest, par value $0.01 per share (“Common Shares”), in one or more private placement transactions exempt from registration under the U.S. Securities Act of 1933, as amended, pursuant to Section 4(a)(2), Regulation D, and/or Regulation S (the “Offering”), including a private placement of Common Shares to certain purchasers that closed prior to the commencement of the Offering (the “Initial Offering”). Prior to the Initial Offering, GCP-PIF Feeder S (“GPIF S Feeder”), a Delaware statutory trust and indirectly wholly-owned subsidiary of GCP HS Fund, purchased 820,400 Common Shares at a price of $25.00 per share (the “Initial Capitalization”). The investment manager for GPIF S Feeder and GCP HS Fund is an affiliate of the Investment Adviser. Prior to the Initial Offering closing, the Board authorized the redemption of all of the Initial Capitalization Common Shares outstanding at a price of $25.00 per share effective December 31, 2025. On December 31, 2025, the Company completed the Initial Offering and accepted subscription agreements for total commitments of $106,828 to purchase the Company’s common shares. On December 31, 2025, the Company received the Initial Offering subscription proceeds and issued 4,273,117 Common Shares at a price of $25.00 per share (the “Initial Closing”). On December 29, 2025, prior to the Company’s election to be regulated as a BDC, the Company entered into a share purchase and sale agreement to acquire its initial portfolio of investments by purchasing 100% of the beneficial interests of each of GPIF S Holdings, GPIF S Funding and PIF Holding Blocker S (the “Initial Assets”) from GCP OS Cayman Trust, a Cayman Islands trust (“OS Cayman Trust”) pursuant to a share purchase and sale agreement by and among the Company, OS Cayman Trust and the Investment Adviser (the “GPIF S Purchase Agreement”). On December 31, 2025, the Company commenced operations and invested proceeds from the Initial Closing to acquire the Initial Assets.

Golub Capital Private Income Fund S (“GPIF S” or the “Company”), is a Delaware statutory trust formed on July 22, 2025. The Company is an externally managed, non-diversified, closed-end management investment company that commenced operations on December 31, 2025, the effective date of the Company’s election to be regulated as a business development company (“BDC”) under the Investment Company Act of 1940, as amended (the “1940 Act”). In addition, for U.S. federal income tax purposes, beginning with its tax year ending September 30, 2026, the Company intends to elect to be treated as a regulated investment company (“RIC”) under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). The Company’s fiscal year end is September 30.

The Company’s investment objective is to generate current income and capital appreciation by investing primarily in privately originated and privately negotiated investments, predominantly through direct lending to U.S. private companies in the middle-market in the form of one stop (a loan that combines characteristics of traditional first lien senior secured loans and second lien or subordinated loans and that are often referred to by other middle-market lenders as unitranche loans) and other senior secured loans. The Company could selectively invest in second lien and subordinated loans (including loans that rank senior only to a borrower’s equity securities and ranks junior to all of such borrower’s other indebtedness in priority of payment) of private companies. The Company also expects to invest in liquid credit instruments, including secured floating rate syndicated loans (e.g., broadly syndicated loans), securitized products and corporate bonds, and the Company’s portfolio may, but will not necessarily, initially be comprised of a greater percentage of such instruments than it will as the Company’s investment program matures, though the exact allocation could vary from time to time depending on market conditions and available investment opportunities. The Company’s portfolio could also include other credit-related investments, including, without limitation, structured and synthetic debt investments and debt investments accompanied by equity securities, preferred equity and, to a limited extent, common equity investments not associated with a debt investment. The Company has entered into an investment advisory agreement dated December 5, 2025 (the “Investment Advisory Agreement”) with GC Advisors, LLC (the “Investment Adviser”), under which the Investment Adviser manages the day-to-day operations of, and provides investment advisory services to, the Company. Under an administration agreement dated December 5, 2025 (the “Administration Agreement”) the Company is provided with certain services by an administrator, which is currently Golub Capital LLC (the “Administrator”).

The Company offers its common shares of beneficial interest, par value $0.01 per share (“Common Shares”), in one or more private placement transactions exempt from registration under the U.S. Securities Act of 1933, as amended, pursuant to Section 4(a)(2), Regulation D, and/or Regulation S (the “Offering”), including a private placement of Common Shares to certain purchasers that closed prior to the commencement of the Offering (the “Initial Offering”).

Prior to the Initial Offering, GCP-PIF Feeder S (“GPIF S Feeder”), a Delaware statutory trust and indirectly wholly-owned subsidiary of GCP HS Fund, purchased 820,400 Common Shares at a price of $25.00 per share (the “Initial Capitalization”). The investment manager for GPIF S Feeder and GCP HS Fund is an affiliate of the Investment Adviser. Prior to the Initial Offering closing, the Board authorized the redemption of all of the Initial Capitalization Common Shares outstanding at a price of $25.00 per share effective December 31, 2025.

On December 29, 2025, prior to the Company’s election to be regulated as a BDC, the Company entered into a share purchase and sale agreement to acquire its initial portfolio of investments by purchasing 100% of the beneficial interests of each of GPIF S Holdings, GPIF S Funding and PIF Holding Blocker S (the “Initial Assets”) from GCP OS Cayman Trust, a Cayman Islands trust (“OS Cayman Trust”) pursuant to a share purchase and sale agreement by and among the Company, OS Cayman Trust and the Investment Adviser (the “GPIF S Purchase Agreement”). On December 31, 2025, the Company commenced operations and invested proceeds from the Initial Closing to acquire the Initial Assets.