8-K

UNITED STATES

SECURITIES AND EXCHANGE

COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of theSecurities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported): January 15, 2026

New Mountain Finance Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (212) 720-0300

None

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

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

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

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. ☐

On January 15, 2026, Alfred F. Hurley, Jr. notified the Board of Directors (the “Board”) of New Mountain Finance Corporation (the “Company”) of his decision to retire from his position as a director of the Company. Mr. Hurley has served as a member of the Board since 2010. Mr. Hurley’s retirement is not the result of any disagreement with the Company. On January 16, 2026, the Company made available on its website a statement announcing Mr. Hurley’s retirement. The text of the statement is included as Exhibit 99.1 to this Form 8-K.

In order to fill the vacancy created by Mr. Hurley’s retirement, the Board appointed John P. Malfettone as a Director of the Company, effective as of January 15, 2026. In connection with his appointment, Mr. Malfettone will also serve as a member of the Audit Committee, Nominating and Corporate Governance Committee, Compensation Committee, and Valuation Committee of the Board. Mr. Malfettone, age 70, has served as a director of NMF SLF I, Inc. since 2019 and as a trustee of New Mountain Private Credit Fund since 2024, each of which is an affiliate of the Company. He has also served as a Senior Advisor to the Transaction Advisory Group at Alvarez & Marsal since 2020. Prior to retirement, he previously served as Senior Managing Director at Clayton, Dubilier & Rice (“CD&R”), a global private investment firm based in New York. Mr. Malfettone joined CD&R in 2010; he was the leader of CD&R’s Portfolio Procurement, Portfolio Insurance Programs, and the Chief Compliance Officer. Previously, from 2004 to 2010, Mr. Malfettone served as a Partner, Chief Operating Officer and Chief Compliance Officer at Oak Hill Capital Partners, a leading U.S. based middle market private equity firm. Prior to joining Oak Hill, he worked for 12 years at General Electric Co. (“GE”) serving numerous leadership roles since 1990, including that of a Managing Director at GE’s private equity business, EVP CFO and Corporate Controller for GE Capital. Before GE, Mr. Malfettone started his career at KPMG in 1977 and was promoted to partner in 1988. Mr. Malfettone has been a CPA since 1978 and earned his Bachelor of Sciences in Accounting, magna cum laude, from the University of Connecticut, where he is a member of the School of Business Hall of Fame. Mr. Malfettone’s charitable endeavors include President of the Cardinal Shehan Center Board and Co-Founder and CEO of Bleeding Blue for Good, the non-profit NIL collective for the University of Connecticut.

There is no arrangement or understanding between Mr. Malfettone and any other persons pursuant to which Mr. Malfettone was selected as a director. There are no family relationships between Mr. Malfettone and any director, executive officer or person nominated or chosen by the Company to become a director or executive officer of the Company within the meaning of Item 401(d) of Regulation S-K under the Securities Act of 1933, as amended (“Regulation S-K”). Mr. Malfettone is not a party to any transaction, or any proposed transaction, required to be disclosed pursuant to Item 404(a) of Regulation S-K.

1

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: January 16, 2026

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Exhibit99.1

After over fifteen years of highly engaged service as an Independent Director, Al Hurley has decided to retire from the Board of New Mountain Finance Corporation (“NMFC”). Al said, “I have very much enjoyed working with a very strong management team that has an extraordinary ability to source, evaluate and invest in very attractive debt transactions as well as to proactively monitor these investments on behalf of our shareholders. While I will miss working with a great team, my retirement from the board will allow me to fulfill my current and upcoming business and civic commitments.” Steve Klinsky, Chairman of the Board of NMFC, said, “We very much appreciated and benefitted from Al’s high quality strategic, market and financial advice throughout his tenure. We will miss Al’s deep engagement with our debt businesses and wish him great success in his current and future endeavors.”