Company: SNY
Filing Date: 2025-10-29
Form Type: 424B5
Source: 0001193125-25-255563
Chunk: 0

Company: Sanofi
Filing Date: 2025-10-29
Form: 424B5
Chunk 0
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Filed pursuant to Rule 424(b)(5)
Registration Statement No. 333-278506

PROSPECTUS SUPPLEMENT

(To Prospectus dated April 4, 2024)

$500,000,000 Floating Rate Notes due 2027

$500,000,000 Floating Rate Notes due 2028

$400,000,000 3.750% Notes due 2027

$400,000,000 3.800% Notes due 2028

$1,200,000,000 4.200% Notes due 2032

The notes offered by this prospectus supplement are (i) the $500,000,000 floating rate notes due 2027 (the “2027 floating rate notes”),
(ii) the $500,000,000 floating rate notes due 2028 (the “2028 floating rate notes” and, together with the 2027 floating rate notes, the “floating rate notes”), (iii) the $400,000,000 3.750% notes due 2027 (the
“2027 fixed rate notes”), (iv) the $400,000,000 3.800% notes due 2028 (the “2028 fixed rate notes”) and (v) the $1,200,000,000 4.200% notes due 2032 (the “2032 fixed rate notes” and together with the
“2027 fixed rate notes” and the “2028 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 2027 floating rate notes and the 2028 floating rate notes will
be 0.460% and 0.540%, respectively. We will pay interest on the floating rate notes on February 3, May 3, August 3 and November 3 of each year, beginning on February 3, 2026. We will pay interest on the fixed rate notes on May 3 and November 3
of each year, beginning on May 3, 2026. Interest on the notes will accrue from November