Free Writing Prospectus (Form FWP)

Filed Pursuant to Rule 433

Issuer Free Writing Prospectus dated September 30, 2025

Relating to Preliminary Prospectus Supplement dated September 30, 2025 and

Prospectus dated April 29, 2024

Registration No. 333-278993

Carlyle Secured Lending, Inc.

$300,000,000 5.750% Notes due 2031

PRICING TERM SHEET

September 30, 2025

The following sets forth the final terms of the 5.750% Notes due 2031 (the "Notes") and should only be read together with the preliminary prospectus supplement dated September 30, 2025 (the "Preliminary Prospectus Supplement") related to the Notes, and supersedes the information in the Preliminary Prospectus Supplement to the extent inconsistent with the information in the Preliminary Prospectus Supplement. In all other respects, this pricing term sheet is qualified in its entirety by reference to the Preliminary Prospectus Supplement. Terms used herein but not defined herein shall have the respective meanings as set forth in the Preliminary Prospectus Supplement. All references to dollar amounts are references to U.S. dollars.

Note: *A securities rating is not a recommendation to buy, sell or hold securities and may be subject to revision or withdrawal at any time.

Note: **Carlyle Secured Lending, Inc. expects that delivery of the Notes will be made to investors on or about October 7, 2025, which will be the fifth business day following the date hereof. Under Rule 15c6-1 under the Exchange Act, trades in the secondary market are required to settle in one business day, unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade notes prior to the business day before the delivery of the Notes will be required, by virtue of the fact that the Notes initially settle in T+5, to specify an alternative arrangement at the time of any such trade to prevent a failed settlement and should consult their own advisors.

Note: *** ICBC Standard Bank Plc is restricted in its U.S. securities dealings under the United States Bank Holding Company Act and may not underwrite, subscribe, agree to purchase or procure purchasers to purchase notes that are offered or sold in the United States. Accordingly, ICBC Standard Bank Plc shall not be obligated to, and shall not, underwrite, subscribe, agree to purchase or procure purchasers to purchase notes that may be offered or sold by other underwriters in the United States. ICBC Standard Bank Plc shall offer and sell the Notes constituting part of its allotment solely outside the United States.

Investors are advised to carefully consider the investment objectives, risks, charges and expenses of Carlyle Secured Lending, Inc. before investing. The Preliminary Prospectus Supplement contains this and other information about Carlyle Secured Lending, Inc. and should be read carefully before investing.

The information in the Preliminary Prospectus Supplement is not complete and may be changed. The Preliminary Prospectus Supplement and this pricing term sheet are not offers to sell any securities of Carlyle Secured Lending, Inc. and are not soliciting an offer to buy such securities in any state or jurisdiction where such offer and sale is not permitted. You may obtain these documents for free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, Carlyle Secured Lending, Inc., any underwriter or any dealer participating in the offering will arrange to send you the Preliminary Prospectus Supplement if you request it from J.P. Morgan Securities LLC, 383 Madison Avenue, New York, New York 10179, Attn: Investment Grade Syndicate Desk, facsimile: 212-834-6081 or by calling at 1-212-834-4533; Barclays Capital Inc., 745 Seventh Avenue, New York, New York 10019, Attention: Syndicate Registration, facsimile: 646-834-8133 or by calling at 1-888-603-5847; BofA Securities, Inc., NC1-022-02-25, 201 North Tryon Street, Charlotte, North Carolina 28255-0001, Attn: Prospectus Department, email: [email protected] or by calling toll-free at 1-800-294-1322; Citigroup Global Markets Inc., c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, New York 11717, Telephone: (800) 831-9146, email: [email protected]; Deutsche Bank Securities Inc., 1 Columbus Circle, New York, New York 10019, Attention: Debt Capital Markets Syndicate, email: [email protected] or by calling at 1-800-503-4611; or Morgan Stanley & Co. LLC, 1585 Broadway, 29th Floor, New York, New York 10036, Attn: Investment Banking Division, facsimile: 203-719-0495 or by calling toll-free at 1-866-718-1649.

Any disclaimers or notices that may appear on this term sheet below the text of this legend are not applicable to this term sheet and should be disregarded. Such disclaimers may have been electronically generated as a result of this term sheet having been sent via, or posted on, Bloomberg or another electronic mail system.