Organization and Basis of Presentation	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Organization Sixth Street Specialty Lending, Inc. (the “Company”) is a Delaware corporation formed on July 21, 2010. The Company was formed primarily to lend to, and selectively invest in, middle-market companies in the United States. The Company has elected to be regulated as a business development company (“BDC”) under the 1940 Act. In addition, for tax purposes, the Company has elected 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 is managed by Sixth Street Specialty Lending Advisers, LLC (the “Adviser”). On June 1, 2011, the Company formed a wholly-owned subsidiary, TC Lending, LLC, a Delaware limited liability company. On March 22, 2012, the Company formed a wholly-owned subsidiary, Sixth Street SL SPV, LLC, a Delaware limited liability company. On May 19, 2014, the Company formed a wholly-owned subsidiary, Sixth Street SL Holding, LLC, a Delaware limited liability company. On December 9, 2020, the Company formed a wholly-owned subsidiary, Sixth Street Specialty Lending Sub, LLC, a Cayman Islands limited liability company. On March 21, 2014, the Company completed its initial public offering (“IPO”) and the Company’s shares began trading on the New York Stock Exchange (“NYSE”) under the symbol “TSLX.” On December 23, 2025, affiliates of Sixth Street, including the Company, and affiliates of Carlyle Group Inc. (“Carlyle”) entered into an amended and restated limited liability company agreement, as amended from time to time (the “Limited Liability Company Agreement”) to co-manage Structured Credit Partners JV, LLC (“SCP”), a joint venture focused on investing in broadly syndicated first lien senior secured loans, financed with long-term, non-mark-to-market, and predominantly investment grade rated CLO debt. The Company has 25.0% voting ownership in SCP and has commitments to fund, from time to time, capital of up to $200.0 million. Refer to Note 6, Fair Value of Financial Instruments, to these consolidated financial statements for further details. Basis of Presentation The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”), and include the accounts of the Company and its subsidiaries. In the opinion of management, all adjustments considered necessary for the fair presentation of the consolidated financial statements for the periods presented have been included. The results of operations for interim periods are not indicative of results to be expected for the full year. All intercompany balances and transactions have been eliminated in consolidation. Certain financial information that is normally included in annual financial statements, including certain financial statement footnotes, prepared in accordance with U.S. GAAP, is not required for interim reporting purposes and has been condensed or omitted herein. These consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements and notes related thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, which was filed with the Securities and Exchange Commission (“SEC”), on February 12, 2026. The Company is an investment company and, therefore, applies the specialized accounting and reporting guidance in Accounting Standards Codification (“ASC”) Topic 946, Financial Services – Investment Companies. Fiscal Year End The Company’s fiscal year ends on December 31.

Organization

Sixth Street Specialty Lending, Inc. (the “Company”) is a Delaware corporation formed on July 21, 2010. The Company was formed primarily to lend to, and selectively invest in, middle-market companies in the United States. The Company has elected to be regulated as a business development company (“BDC”) under the 1940 Act. In addition, for tax purposes, the Company has elected 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 is managed by Sixth Street Specialty Lending Advisers, LLC (the “Adviser”).

On June 1, 2011, the Company formed a wholly-owned subsidiary, TC Lending, LLC, a Delaware limited liability company.

On March 22, 2012, the Company formed a wholly-owned subsidiary, Sixth Street SL SPV, LLC, a Delaware limited liability company.

On May 19, 2014, the Company formed a wholly-owned subsidiary, Sixth Street SL Holding, LLC, a Delaware limited liability company.

On December 9, 2020, the Company formed a wholly-owned subsidiary, Sixth Street Specialty Lending Sub, LLC, a Cayman Islands limited liability company.

On March 21, 2014, the Company completed its initial public offering (“IPO”) and the Company’s shares began trading on the New York Stock Exchange (“NYSE”) under the symbol “TSLX.”

On December 23, 2025, affiliates of Sixth Street, including the Company, and affiliates of Carlyle Group Inc. (“Carlyle”) entered into an amended and restated limited liability company agreement, as amended from time to time (the “Limited Liability Company Agreement”) to co-manage Structured Credit Partners JV, LLC (“SCP”), a joint venture focused on investing in broadly syndicated first lien senior secured loans, financed with long-term, non-mark-to-market, and predominantly investment grade rated CLO debt. The Company has 25.0% voting ownership in SCP and has commitments to fund, from time to time, capital of up to $200.0 million. Refer to Note 6, Fair Value of Financial Instruments, to these consolidated financial statements for further details.

Basis of Presentation

The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”), and include the accounts of the Company and its subsidiaries. In the opinion of management, all adjustments considered necessary for the fair presentation of the consolidated financial statements for the periods presented have been included. The results of operations for interim periods are not indicative of results to be expected for the full year. All intercompany balances and transactions have been eliminated in consolidation.

Certain financial information that is normally included in annual financial statements, including certain financial statement footnotes, prepared in accordance with U.S. GAAP, is not required for interim reporting purposes and has been condensed or omitted herein. These consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements and notes related thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, which was filed with the Securities and Exchange Commission (“SEC”), on February 12, 2026.

The Company is an investment company and, therefore, applies the specialized accounting and reporting guidance in Accounting Standards Codification (“ASC”) Topic 946, Financial Services – Investment Companies.