GOLUB CAPITAL BDC, Inc.

PART I

In this Annual Report on Form 10-K, except as otherwise indicated, the terms:

•“we,” “us,” “our”, “Company” and “Golub Capital BDC” refer to Golub Capital BDC, Inc., a Delaware corporation, and its consolidated subsidiaries;

•“BDC Holdings” refers to Golub Capital BDC Holdings LLC, a Delaware limited liability company, or LLC, our direct subsidiary;

•“GCIC Holdings” refers to GCIC Holdings LLC, a Delaware LLC, our direct subsidiary;

•“2018 Issuer” refers to Golub Capital BDC CLO III LLC, a Delaware LLC, our indirect subsidiary;

•“GCIC 2018 Issuer" refers to GCIC CLO II LLC, a Delaware LLC, our indirect subsidiary;

•“2018 CLO Depositor” refers to Golub Capital BDC CLO III Depositor LLC, a Delaware LLC, our direct subsidiary;

•“GCIC 2018 CLO Depositor” refers to GCIC CLO II Depositor LLC, a Delaware LLC, our direct subsidiary;

•“GBDC CLO 8 Depositor” refers to Golub Capital BDC CLO 8 Depositor LLC, a Delaware LLC, our direct subsidiary;

•“2024 Issuer” refers to Golub Capital BDC CLO 8 LLC, a Delaware LLC, our indirect subsidiary;

•“GBDC 3 Holdings” refers to GBDC 3 Holdings LLC, a Delaware limited liability company, or LLC, our direct subsidiary;

•“GBDC 3 2021 CLO Depositor” refers to Golub Capital BDC 3 CLO 1 Depositor LLC, a Delaware LLC, our direct subsidiary;

•“GBDC 3 2021 Issuer” refers to Golub Capital BDC 3 CLO 1 LLC, a Delaware LLC, our indirect subsidiary;

•“GBDC 3 2022 ABS 2022-1 Depositor” refers to Golub Capital BDC 3 ABS 2022-1 Depositor LLC, a Delaware LLC, our direct subsidiary;

•“GBDC 3 2022 Issuer” refers to Golub Capital BDC 3 ABS 2022-1 LLC, a Delaware LLC, our indirect subsidiary;

•“GBDC 3 2022 CLO 2 Depositor” refers to Golub Capital BDC 3 CLO 2 Depositor LLC, a Delaware LLC, our direct subsidiary;

•“GBDC 3 2022-2 Issuer” refers to Golub Capital BDC 3 CLO 2 LLC, a Delaware LLC, our indirect subsidiary;

•“Funding II” refers to Golub Capital BDC Funding II LLC, a Delaware LLC, our direct subsidiary;

•“Funding Subsidiaries” refers, collectively, to Funding II, prior to its termination on September 16, 2022; GCIC Funding, prior to its termination on April 30, 2025; GBDC 3 Funding LLC, or GBDC 3 Funding, a Delaware LLC and our direct subsidiary, and each, a “Funding Subsidiary”;

•“2024 Notes” refers to the $400.0 million in aggregate principal amount of unsecured notes issued by Golub Capital BDC on October 2, 2020. The 2024 Notes bore interest at a rate of 3.375% per year payable semiannually in arrears on April 15 and October 15 of each year. The 2024 Notes matured on April 15, 2024. On October 15, 2021, Golub Capital BDC issued an additional $100.0 million in aggregate principal amount of 2024 Notes, which have the same terms as the original issuance of 2024 Notes, other than the issue date and the issue price. On April 8, 2024, the Company redeemed $500.0 million in aggregate principal amount of 2024 Notes under the same terms of the original issuance;

•“2026 Notes” refers to the $400.0 million in aggregate principal amount of unsecured notes issued by Golub Capital BDC on February 24, 2021. The 2026 Notes bear interest at a rate of 2.500% per year payable semiannually in arrears on February 24 and August 24 of each year. The 2026 Notes mature on August 24, 2026. On October 13, 2021, Golub Capital BDC issued an additional $200.0 million in aggregate principal amount of 2026 Notes, which have the same terms as the original issuance of 2026 Notes other than the issue date and the issue price;

•“2027 Notes” refers to the $350.0 million in aggregate principal amount of unsecured notes issued by Golub Capital BDC on August 3, 2021. The 2027 Notes bear interest at a rate of 2.050% per year payable semiannually in arrears on February 15 and August 15 of each year. The 2027 Notes mature on February 15, 2027;

•“2028 Notes” refers to the $450.0 million in aggregate principal amount of unsecured notes issued by Golub Capital BDC on December 5, 2023. The 2028 Notes bear interest at a rate of 7.050% per year payable semiannually in arrears on June 5 and December 5 of each year. The 2028 Notes mature on December 5, 2028. On September 19, 2025, Golub Capital BDC issued an additional $250.0 million in aggregate principal amount of 2028 Notes, which have the same terms as the original issuance of 2028 Notes, other than the issue date and the issue price;

•“2029 Notes” refers to the $600.0 million in aggregate principal amount of unsecured notes issued by Golub Capital BDC on February 1, 2024. The 2029 Notes bear interest at a rate of 6.000% per year payable semiannually in arrears on January 15 and July 15 of each year. The 2029 Notes mature on July 15, 2029. On December 3, 2024, Golub Capital BDC issued an additional $150.0 million in aggregate principal amount of 2029 Notes, which have the same terms as the original issuance of 2029 Notes, other than the issue date and the issue price;

•“Unsecured Notes” refers, collectively, to the 2024 Notes, 2026 Notes, 2027 Notes, 2028 Notes and 2029 Notes;

•“GCIC” refers to Golub Capital Investment Corporation, a Maryland corporation that we acquired on September 16, 2019 pursuant to an agreement and plan of merger by and among us, GCIC, GC Advisors, and for certain limited purposes our Administrator (as defined below), or, as amended, the GCIC Merger Agreement; prior to such acquisition, which we refer to as the GCIC Merger, GCIC was an externally managed, closed-end, non-diversified management investment company that elected to be regulated as a business development company under the Investment Company Act of 1940, as amended, or the 1940 Act, and whose investment adviser was GC Advisors. GCIC’s common stock was converted into the right to receive 0.865 shares of our common stock (with GCIC’s stockholders receiving cash in lieu of fractional shares of our common stock), and we issued an aggregate 71,779,964 shares of our common stock to former stockholders of GCIC;

•“GBDC 3” refers to Golub Capital BDC 3, a Maryland corporation that we acquired on June 3, 2024 pursuant to an agreement and plan of merger by and among us, GBDC 3, GC Advisors, and for certain limited purposes our Administrator, or, as amended, the GBDC 3 Merger Agreement; prior to such acquisition, which we refer to as the GBDC 3 Merger, GBDC 3 was an externally managed, closed-end, non-diversified management investment company that elected to be regulated as a business development company under the Investment Company Act of 1940, as amended, or the 1940 Act, and whose investment adviser was GC Advisors. GBDC 3’s common stock was converted into the right to receive 0.914 shares of our common stock (with GBDC 3’s stockholders receiving cash in lieu of fractional shares of our common stock), and we issued an aggregate 92,115,308 shares of our common stock to former stockholders of GBDC 3;

•“2024 Debt Securitization” refers to the $2,200.5 million term debt securitization that we completed on November 18, 2024, in which the 2024 Issuer issued an aggregate of $2,200.5 million of notes, or the “2024 Notes,” including $1,192.4 million of Class A-1R 2024 Notes, which bear interest at a rate of three-month Term SOFR, plus 1.56%, $171.6 million of Class A-2RR 2024 Notes, which bear interest at a rate of three-month Term SOFR, plus 1.75%, $165.0 million of Class B-R 2024 Notes, which bear interest at a rate of three-month Term SOFR, plus 1.70%, $154.0 million of Class C-R, which bear interest at a rate of three-month Term SOFR, plus 2.10%, and $517.5 million of Subordinated Notes that do not bear interest;

•“2018 Debt Securitization” refers to the $602.4 million term debt securitization that we completed on November 16, 2018, and redeemed on November 18, 2024, in which the 2018 Issuer issued an aggregate of $602.4 million of notes, or the “2018 Notes,” including $327.0 million of Class A 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 1.48%, $61.2 million of Class B 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.10%, $20.0 million of Class C-1 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.80%, $38.8 million of Class C-2 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.65%, $42.0 million of Class D 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.95%, and $113.4 million of Subordinated 2018 Notes that did not bear interest;

•“GCIC 2018 Debt Securitization” refers to the $908.2 million term debt securitization initially completed on December 13, 2018 and that we acquired as part of the GCIC Merger, and redeemed on November 18, 2024, in which the GCIC 2018 Issuer issued an aggregate of $908.2 million of notes, or the “GCIC 2018 Notes”, including $490.0 million of AAA/AAA Class A-1 GCIC 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 1.48%, $38.5 million of AAA Class A-2 GCIC 2018 Notes, which bore interest at a fixed rate of 4.67%, $18.0 million of AA Class B-1 GCIC 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.25%, $27.0 million of the Class B-2 GCIC 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 1.75%, $95.0 million of Class C GCIC 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.30%, $60.0 million of Class D GCIC 2018 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.75% and $179.7 million of Subordinated GCIC 2018 Notes that did not bear interest;

•“GBDC 3 2021 Debt Securitization” refers to the $398.9 million term debt securitization initially completed on March 11, 2021 and that we acquired as part of the GBDC 3 Merger, and redeemed on November 18, 2024, in which the GBDC 3 2021 Issuer issued an aggregate of $398.9 million of notes, or the “GBDC 3 2021 Notes”, including $224.0 million of AAA Class A GBDC 3 2021 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 1.60%, $28.0 million of AA Class B GBDC 3 2021 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 1.85%, $36.0 million of A Class C-1 GBDC 3 2021 Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.80%, $10.0 million of the A Class C-2 GBDC 3 2021 Notes, which bore interest at a fixed rate of 3.91% and $100.9 million of Subordinated GBDC 3 2021 Notes that did not bear interest;

•“GBDC 3 2022 Debt Securitization” refers to the $401.8 million term debt securitization initially completed on January 25, 2022 and that we acquired as part of the GBDC 3 Merger, and redeemed on August 1, 2025, in which the GBDC 3 2022 Issuer issued an aggregate of $401.8 million of notes, or the “GBDC 3 2022 Notes”, including $252.0 million of Class A Senior Secured Floating Rate Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.00% and $149.8 million of Subordinated Notes that did not bear interest;

•“GBDC 3 2022-2 Debt Securitization” refers to the $386.6 million term debt securitization initially completed on December 14, 2022 and that we acquired as part of the GBDC 3 Merger, and redeemed on December 16, 2024, in which the GBDC 3 2022-2 Issuer issued an aggregate of $386.6 million of notes, or the “GBDC 3 2022-2 Notes”, including $140.0 million of AAA Class A GBDC 3 Senior Secured Floating Rates Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.60%, $38.8 million of AA Class B GBDC 3 Senior Secured Floating Rates Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 3.09%, $85.0 million of AAA Class A GBDC 3 Senior Secured Floating Rates Notes, which bore interest at a rate of three-month Term SOFR, plus 0.26161%, plus 2.60% and $122.8 million of Subordinated Notes that did not bear interest;

•“Debt Securitizations” refers collectively to the 2024 Debt Securitization, and prior to its termination on August 1, 2025, the GBDC 3 2022 Debt Securitization, and prior to its termination on December 16, 2024, GBDC 3 2022-2 Debt Securitization, and prior to their respective terminations on November 18, 2024, the 2018 Debt Securitization, GCIC 2018 Debt Securitization, and the GBDC 3 2021 Debt Securitization, and each, a “Debt Securitization;”

•“GBDC 3 DB Credit Facility” refers to the senior secured revolving credit facility that GBDC 3 Funding entered into on September 10, 2019 and terminated on November 19, 2024, with GBDC 3, as equity holder and as servicer, Deutsche Bank AG, New York Branch, as facility agent, the other agents parties thereto, each of the entities from time to time party thereto as securitization subsidiaries and Deutsche Bank Trust Company Americas, as collateral agent and as collateral custodian, that, as of the date of termination, allowed for borrowing up to $625.0 million in U.S. dollars and bore interest at a rate of the applicable base rate plus 2.30% per annum;

•“JPM Credit Facility” refers to the senior secured revolving credit facility that we initially entered into on February 11, 2021 with JPMorgan Chase Bank, N.A. as administrative agent and collateral agent, and the bank participants acting as lenders, as amended, that, as of September 30, 2025, permits borrowings of up to $1,998 million in U.S. dollars and certain agreed upon foreign currencies. As of September 30, 2025, the interest rate on the borrowings under the facility ranged from the applicable benchmark plus 1.525% to 1.775%, depending on the gross borrowing base, through the maturity date of April 4, 2030. The applicable benchmark rate as of September 30, 2025 for loans denominated in U.S. dollars is one-month SOFR plus an adjustment of 0.10% and certain other benchmark rates for loans denominated in other foreign currencies;

•“Revolving Credit Facilities” refers collectively to, prior to its termination on November 19, 2024, the GBDC 3 DB Credit Facility and the JPM Credit Facility, each a “Revolving Credit Facility”;

•“Adviser Revolver” refers to the line of credit with GC Advisors, which allowed for borrowing up to $300.0 million and bears interest at the mid-term applicable federal rate, as of September 30, 2025 ;

•“GC Advisors” refers to GC Advisors LLC, a Delaware LLC, our investment adviser;

•“Administrator” refers to Golub Capital LLC, a Delaware LLC, an affiliate of GC Advisors and our administrator;

•“Investment Advisory Agreement” or “Post-GBDC 3 Merger Advisory Agreement” refers to the Fifth Amended and Restated Investment Advisory Agreement by and between us and GC Advisors, dated and effective as of June 3, 2024;

•“Prior Investment Advisory Agreement” refers to the Fourth Amended and Restated Investment Advisory Agreement by and between us and GC Advisors, dated as of August 3, 2023 and effective as of July 1, 2023; and

•“Golub Capital” refers, collectively, to the activities and operations of Golub Capital LLC (formerly Golub Capital Management LLC), which entity employs all of Golub Capital’s investment professionals, GC Advisors and associated investment funds and their respective affiliates.