Bain Capital Specialty Finance, Inc.

F1,

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

For the fiscal year ended December 31,2025

OR

For the transition period from __ to __

Commission file number:814-01175

BAIN CAPITAL SPECIALTY FINANCE, INC.

(Exact Name of Registrant as Specified in its Charter)

(617)516‑2000

(Registrant’s Telephone Number, Including Area Code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐No ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ☐No ☒

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically, and every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b‑2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report.☒

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b‑2 of the Act). Yes ☐ No☒

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant, was$664.7 million based on the number of shares held by non-affiliates of the registrant as of December 31, 2025. Shares of the registrant’s common stock held by each executive officer, director and holder of 5% or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose. As of February 26, 2026,64,868,507 shares of common stock were outstanding.

Documents Incorporated by Reference

Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2026 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III

of this Form 10-K where indicated. Such definitive proxy statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the registrant’s fiscal year ended December 31, 2025.

TABLE OF CONTENTS

i

CERTAIN DEFINITIONS

Except as otherwise specified in this Annual Report on Form 10-K (“Annual Report”), the terms “we,” “us,” “our”, and the “Company” refer to Bain Capital Specialty Finance, Inc.

FORWARD-LOOKING STATEMENTS

Statements contained in this Annual Report (including those relating to current and future market conditions and trends in respect thereof) that are not historical facts are based on current expectations, estimates, projections, opinions and/or beliefs of the Company, BCSF Advisors, LP (the “Advisor”) and/or Bain Capital Credit, LP and its affiliated advisers (collectively, “Bain Capital Credit”). Such statements involve known and unknown risks, uncertainties and other factors and undue reliance should not be placed thereon. Certain information contained in this Annual Report constitutes “forward-looking statements,” which can be identified by the use of forward-looking terminology such as “may,” “will,” “should,” “seek,” “expect,” “anticipate,” “project,” “estimate,” “intend,” “continue,” “target,” or “believe” or the negatives thereof or other variations thereon or comparable terminology. Due to various risks and uncertainties, actual events or results or the actual performance of the Company may differ materially from those reflected or contemplated in such forward-looking statements. These statements are not guarantees of future performance and are subject to risks, uncertainties, and other factors, some of which are beyond our control and are difficult to predict, that could cause actual results to differ materially from those expressed or forecasted in the forward-looking statements including, without limitation, the risks, uncertainties and other factors we identify in the section entitled “Item 1A. Risk Factors” and elsewhere in this Annual Report and in our filings with the Securities and Exchange Commission (the “SEC”).

Although we believe that the assumptions on which these forward-looking statements are based are reasonable, some of those assumptions may be based on the work of third parties and any of those assumptions could prove to be inaccurate; as a result, the forward-looking statements based on those assumptions also could prove to be inaccurate. In light of these and other uncertainties, the inclusion of a projection or forward-looking statement in this Annual Report should not be regarded as a representation by us that our plans and objectives will be achieved. These risks and uncertainties include those described or identified in the section entitled “Item 1A. Risk Factors” and elsewhere in this Annual Report. Investors should not place undue reliance on these forward-looking statements, which apply only as of the date of this Annual Report. We do not undertake any obligation to update or revise any forward-looking statements or any other information contained herein, except as required by applicable law. The safe harbor provisions of Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), which preclude civil liability for certain forward-looking statements, do not apply to the forward-looking statements in this Annual Report because we are an investment company.