Company: SNY
Filing Date: 2025-10-27
Form Type: 424B5
Source: 0001193125-25-250786
Chunk: 0

Company: Sanofi
Filing Date: 2025-10-27
Form: 424B5
Chunk 0
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Filed pursuant to Rule 424(b)(5)
Registration Statement No. 333-278506

The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has become effective upon filing with the Securities and Exchange Commission. We are not using this prospectus supplement or the attached prospectus to offer to sell these securities or to solicit offers to buy these securities in any place where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED October 27, 2025

PROSPECTUS SUPPLEMENT

(To Prospectus dated April 4, 2024)

$ Floating Rate Notes due 20

$ Floating Rate Notes due 20

$ % Notes due 20

$ % Notes due 20

$ % Notes due 20

The notes offered by this prospectus supplement are (i) the $ floating rate notes due 20 (the “
20 floating rate notes”), (ii) the $ floating rate notes due 20 (the “ 20 floating rate notes” and, together with the 20 floating
rate notes, the “floating rate notes”), (iii) the $ % notes due 20 (the “20 fixed rate notes”), (iv) the $ % notes due
20 (the “20 fixed rate notes”) and (v) the $ % notes due 20 (the “20 fixed rate notes” and together with the
“20 fixed rate notes” and the “20 fixed rate notes,” the “fixed rate notes”). We refer to the floating rate notes and the fixed rate notes collectively as the
“notes.”

The floating rate notes will bear interest at an interest rate for each interest period equal to Compounded SOFR (as defined
herein), reset quarterly, plus a margin, subject to the provisions set forth in the “Description of the Notes—Principle, Interest and Maturity—Floating Rate Notes.” The margin applicable to the 20 floating
rate notes and the 20 floating rate notes will be % and %, respectively. We will pay interest on the floating rate notes
on , , and of each year, beginning on , 2026. We will pay interest on the fixed rate notes
on and of each year, beginning on , 2026. Interest on the notes will accrue from , 2025. The 20 floating rate notes, the
20 floating rate notes, the 20 fixed rate notes, the 20 fixed rate notes and the