Item 1.01. Entry into a Material Definitive Agreement. On March 28, 2025, New Mountain Finance Corporation (the“ Company”) entered into the Thirteenth Amendment to Loan and Security Agreement (the“ Thirteenth Amendment”), which amended the Third Amended and Restated Loan and Security Agreement, dated as of October 24, 2017 (together with the exhibits and schedules thereto, the “ Loan and Security Agreement”), by and among New Mountain Finance Holdings, L. L. C., as borrower, the Company, as collateral manager, Wells Fargo Bank, National Association (“ Wells Fargo”), as administrative agent, a lender, and swingline lender, the lenders party thereto from time to time, and Wells Fargo, as collateral custodian. Unless otherwise indicated, the terms used below have the meanings ascribed in the Loan and Security Agreement.

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The disclosure set forth above under Item 1.01 is incorporated by reference herein.

Item 9.01 Financial Statements and Exhibits (d) Exhibits. Exhibit No. 104 Cover Page Interactive Data 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. New Mountain Finance Corporation By: /s/ Eric Kane Name: Eric Kane Title: Corporate Secretary Date: April 2, 2025