Sixth Street Specialty Lending, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(RULE

14a-101)

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant ☒ Filed by a Party other than the Registrant ☐

Check the appropriate box:

(Name of Registrant as Specified in Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

April 10, 2025

To Our Stockholders:

We are pleased to invite you to attend the 2025 Annual Meeting of Stockholders of Sixth Street Specialty Lending, Inc. to be held on May 22, 2025, at 9:30 a.m., Eastern Time, at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017.

The following pages include a formal notice of the meeting and our proxy statement. The Notice of Internet Availability of Proxy Materials that you received by mail and this proxy statement describe various matters on the agenda for the meeting. Please read these materials so that you will know what we plan to do at the meeting. It is important that your shares be represented at the annual meeting, regardless of whether you plan to attend the meeting in person. Please vote your shares as soon as possible through any of the voting options available to you as described in the Notice of Internet Availability of Proxy Materials and this proxy statement.

You will also receive separate proxy materials for a Special Meeting of Stockholders, which will be held at the same place and on the same date stated above, but not at the same time. Please be certain to use each proxy card that you receive from us to vote separately for the matters to be discussed at each meeting.

On behalf of management and our Board of Directors, we thank you for your continued support of Sixth Street Specialty Lending, Inc.

Sincerely,

/s/ Joshua Easterly

Chairman of the Board of Directors

Important Notice Regarding the Availability of Proxy Material for the Annual Meeting of Stockholders to Be Held on May 22, 2025.

Our proxy statement and annual report on Form 10-K for the year ended December 31, 2024 are available online at www.proxyvote.com.

The following information applicable to the Annual Meeting of Stockholders may be found in the proxy statement and accompanying proxy card:

Notice of the 2025 Annual Meeting of Stockholders

TO OUR STOCKHOLDERS:

NOTICE IS HEREBY GIVEN that the 2025 Annual Meeting of Stockholders of Sixth Street Specialty Lending, Inc. will be held at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017 on May 22, 2025, at 9:30 a.m., Eastern Time. The 2025 Annual Meeting of Stockholders is being held for the following purposes:

1. To elect three Class II directors, each to serve for a three-year term and until a successor has been duly elected and qualified or until the director’s earlier resignation or removal.

2. To ratify the selection of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025.

3. To transact such other business as may properly come before the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof.

Only stockholders of record at the close of business on March 31, 2025, are entitled to notice of and to vote at the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof.

We are furnishing a proxy statement, annual report and proxy card to our stockholders on the internet, rather than mailing printed copies of those materials to each stockholder. If you received a Notice of Internet Availability of Proxy Materials by mail, you will not receive a printed copy of the proxy statement, annual report and proxy card unless you request them. Instead, the Notice of Internet Availability of Proxy Materials will instruct you as to how you may access and review the proxy statement and annual report, and vote your proxy, on the internet.

Your vote is extremely important to us. Whether or not you plan to attend the 2025 Annual Meeting of Stockholders, we encourage you to vote your proxy on the internet by following the instructions provided on the Notice of Internet Availability of Proxy Materials or proxy card. Stockholders may also request from us, free of charge, hard copies of the proxy statement and proxy card by following the instructions on the Notice of Internet Availability of Proxy Materials.

Further, from time to time, we may repurchase shares of our common stock and are notifying you of this ability as required by applicable securities law. See “Stock Repurchases” in the proxy statement.

By Order of the Board of Directors,

/s/ Anton Brett

Anton Brett

Chief Compliance Officer and Secretary

April 10, 2025

YOUR VOTE IS IMPORTANT! WE HOPE YOU WILL VOTE OVER THE INTERNET, BY PHONE OR BY MARKING, SIGNING AND RETURNING YOUR PROXY CARD AS SOON AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE MEETING. EVEN IF YOU VOTE YOUR SHARES PRIOR TO THE MEETING, YOU STILL MAY ATTEND THE MEETING AND VOTE YOUR SHARES IN PERSON.

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