Company: NNN
Filing Date: 2025-06-24
Form Type: 424B5
Source: 0001193125-25-145374
Chunk: 0

Company: NNN REIT, INC.
Filing Date: 2025-06-24
Form: 424B5
Chunk 0
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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-273605 This preliminary prospectus supplement relates to an effective shelf registration statement under the Securities Act of 1933, as amended, but is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED JUNE 24, 2025 PRELIMINARY PROSPECTUS SUPPLEMENT (To Prospectus dated August 2, 2023) $ % Notes due We are offering $ aggregate principal amount of % notes due . The notes will have the following terms:

| • |     | Interest on the notes will be payable semi-annually on and    , commencing    , 2026. |

| • |     | The notes mature on     , and will be redeemable in whole or in part at any time or from time to                                         
 time at the redemption price described in the section of this prospectus supplement entitled “Description of Notes—Optional Redemption.” |

| • |     | There is no sinking fund for the notes. |

| • |     | The notes will be our senior unsecured obligations and will rank equally with all of our other senior indebtedness from                                                                                                                                   
 time to time outstanding. However, the notes will be effectively subordinated to our mortgage debt and other secured indebtedness (to the extent of the value of the assets securing such debt) and will be structurally subordinated to the indebtedness 
 and other liabilities of our subsidiaries (to the extent of the value of the assets of those subsidiaries), if any.                                                                                                                                       |

| • |     | The notes will be a new series of securities with no established trading market. The notes will not be listed on any 
 securities exchange or automated quotation system.                                                                   |

Investing in the notes involves risks. See “ Risk Factors” beginning on page S-4of this prospectus supplement, page 6 of the accompanying prospectus and page 9 of our Annual Report on Form 10-Kfor the fiscal year ended December 31, 2024, which is incorporated herein by reference.

|                                                 |     | Per Note |     |   |     | Total |
|:------------------------------------------------|:----|:---------|:----|:--