Exhibit (l)

	Simpson Thacher & Bartlett LLP
	900 G STREET, NW WASHINGTON, D.C. 20001
	TELEPHONE: +1-202-636-5500 FACSIMILE: +1-202-636-5502
Direct Dial Number		E-mail Address

December 22, 2023

Sixth Street Specialty Lending, Inc.

2100 McKinney Avenue, Suite 1500

Dallas, TX 75201

Ladies and Gentlemen:

We have acted as counsel to Sixth Street Specialty Lending, Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form N-2 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, relating to (i) shares of common stock of the Company, par value $0.01 per share (the “Common Stock”); (ii) shares of preferred stock of the Company, par value $0.01 per share (the “Preferred Stock”); (iii) debt securities, which may be either senior debt securities or subordinated debt securities and which may be convertible into other securities of the Company (collectively, the “Debt Securities”); (iv) warrants to purchase Common Stock, Preferred Stock or Debt Securities (the “Warrants”); and (v) subscription rights to purchase Common Stock (the “Subscription Rights”). The Common Stock, the Preferred Stock, the Debt Securities, the Warrants and the Subscription Rights are hereinafter referred to collectively as the “Securities.” The Securities may be issued and sold or delivered from time to time for an indeterminate aggregate initial offering price.

Sixth Street Specialty Lending, Inc. December 22, 2023

The Debt Securities will be issued under an Indenture (the “Indenture”) between the Company and a trustee named therein.

The Warrants will be issued pursuant to one or more warrant agreements (each, a “Warrant Agreement”) between the Company and a warrant agent named therein.

The Subscription Rights will be issued pursuant to one or more subscription rights agreements (each, a “Rights Agreement”) between the Company and a rights agent named therein.

The Indenture (including any supplemental indentures thereto), the Warrant Agreements and the Rights Agreements are hereinafter collectively referred to as the “Securities Agreements.”

We have examined the Registration Statement and the form of Indenture. In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and have made such other investigations as we have deemed relevant and necessary in connection with the opinions hereinafter set forth.

In rendering the opinions set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies, and the authenticity of the originals of such latter documents. We also have assumed that, at the time of execution, authentication, issuance and delivery of any of the Securities, the applicable Securities Agreement will be the valid and legally binding obligation of each party thereto other than the Company. We also have assumed that, with respect to the issuance of any shares of Common Stock or Preferred Stock, the amount of valid consideration paid in respect of such shares will equal or exceed the par value of such shares.

Sixth Street Specialty Lending, Inc. December 22, 2023

In rendering the opinions set forth below, we have assumed further that, at the time of execution, authentication, issuance and delivery, as applicable, of each of the applicable Securities Agreements and Securities, (1) the Company will be validly existing and in good standing under the law of the jurisdiction in which it is organized and such Securities Agreement will have been duly authorized, executed and delivered by the Company in accordance with its organizational documents and the law of the jurisdiction in which it is organized, (2) the execution, delivery, issuance and performance, as applicable, by the Company of such Securities Agreement and such Securities will not constitute a breach or violation of its organizational documents or violate the law of the jurisdiction in which it is organized or any other jurisdiction (except that no such assumption is made with respect to the law of the State of New York or the Delaware General Corporation Law, assuming there shall not have been any change in such law affecting the validity or enforceability of such Securities Agreement and such Securities) and (3) the execution, delivery, issuance and performance, as applicable, by the Company of such Securities Agreement and such Securities (a) will not constitute a breach or default under any agreement or instrument which is binding upon the Company or and (b) will comply with all applicable regulatory requirements.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that:

1. With respect to the Common Stock, assuming (a) the taking by the Board of Directors of the Company or a duly constituted and acting committee of such Board of Directors (such Board of Directors or committee being referred to herein as the “Board”) of all necessary corporate action to authorize and approve the issuance of the Common Stock and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) due issuance and delivery

Sixth Street Specialty Lending, Inc. December 22, 2023

of the Common Stock, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Board and otherwise in accordance with the provisions of such agreement, the Company’s Restated Certificate of Incorporation, dated June 15, 2020 (the “Certificate of Incorporation”), the Company’s Second Amended and Restated Bylaws, dated July 10, 2023 (the “Bylaws”) and the Delaware General Corporation Law, the Common Stock will be validly issued, fully paid and nonassessable.

2. With respect to the Preferred Stock, assuming (a) the taking by the Board of all necessary corporate action to authorize and approve the issuance and terms of the Preferred Stock and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company, (b) due filing of the applicable definitive certificate of designations with respect to such Preferred Stock and (c) due issuance and delivery of the Preferred Stock, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Board and otherwise in accordance with the provisions of such agreement, the Certificate of Incorporation, the Bylaws and the Delaware General Corporation Law, the Preferred Stock will be validly issued, fully paid and nonassessable.

3. With respect to the Debt Securities, assuming (a) the taking of all necessary corporate action by the Board, or, unless the Debt Securities are convertible into equity securities of the Company, duly authorized officers of the Company (such Board or authorized officers being referred to herein as the “Company Authorizing Party”) to authorize and approve the issuance and terms of any Debt Securities and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) the due execution, authentication, issuance and delivery of such Debt Securities, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Company Authorizing Party and otherwise in accordance with the provisions of such agreement and the applicable Indenture, such Debt Securities will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

4. With respect to the Warrants, assuming (a) the taking of all necessary corporate action by the Board to authorize and approve the issuance and terms of any Warrants and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) the due execution, countersignature, issuance and delivery of such Warrants, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Board and otherwise in accordance with the provisions of such agreement and the applicable definitive Warrant Agreement, such Warrants will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Sixth Street Specialty Lending, Inc. December 22, 2023

5. With respect to the Subscription Rights, assuming (a) the taking of all necessary corporate action by the Board to authorize and approve the issuance and terms of the Subscription Rights and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) the due execution, countersignature, issuance and delivery of such Subscription Rights, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Board and otherwise in accordance with the provisions of such agreement and the applicable definitive Subscription Rights Agreement, such Subscription Rights will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Our opinions set forth in paragraphs 3 through 5 above are subject to (i) the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, (ii) general equitable principles (whether considered in a proceeding in equity or at law) and (iii) an implied covenant of good faith and fair dealing. In addition, we express no opinion as to the validity, legally binding effect or enforceability of the waiver of rights and defenses contained in Section 3.06 of the Indenture. In connection with the provisions of the Indenture whereby the parties will submit to the jurisdiction of the courts of the United States of America for the Southern District of New York, we note the limitations of 28 U.S.C. Sections 1331 and 1332 on subject matter jurisdiction of the federal courts.

We do not express any opinion herein concerning any law other than the law of the State of New York and the Delaware General Corporation Law.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the use of our name under the caption “Legal Matters” in the Prospectus included in the Registration Statement.

Very truly yours,

/s/ Simpson Thacher & Bartlett LLP

SIMPSON THACHER & BARTLETT LLP