Company: SNY
Filing Date: 2025-10-29
Form Type: 424B5
Source: 0001193125-25-255563
Chunk: 3

Company: Sanofi
Filing Date: 2025-10-29
Form: 424B5
Chunk 3
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 99.744 | % |
| Total                       |     | $                   |   399,976,000 |   |     | $            | 1,000,000 |   |     | $                |   398,976,000 |   |
| Per 2032 Fixed Rate Note    |     |                     |        99.790 | % |     |              |     0.350 | % |     |                  |        99.440 | % |
| Total                       |     | $                   | 1,197,480,000 |   |     | $            | 4,200,000 |   |     | $                | 1,193,280,000 |   |

| (1) | Plus accrued interest from November 3, 2025 if settlement occurs after that date. |

None of the Securities and Exchange Commission, any state securities commission or any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the attached prospectus. Any representation to the contrary is a criminal offense. The underwriters will deliver the notes to purchasers in book-entry form only through the facilities of The Depository Trust Company (“DTC”) for the accounts of its direct and indirect participants (including Euroclear S.A./N.V. (“Euroclear”), as operator of the Euroclear System, and Clearstream Banking S.A. (“Clearstream”)) against payment, expected to occur on or about November 3, 2025. Global Coordinators and Joint Book-Running Managers

| Barclays |     | BNP PARIBAS |     | BofA Securities |

Joint Book-Running Managers

| J.P. Morgan |     | Morgan Stanley |     | MUFG |     | Natixis |

The date of this prospectus supplement is October 27, 2025.

TABLE OF CONTENTS Prospectus Supplement

|                                                           |     | Page |      |
| CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS |     |      | S-1  |
| INCORPORATION OF INFORMATION WE FILE WITH THE SEC         |     |      | S-4  |
| SUMMARY                                                   |     |      | S-6  |
| THE OFFERING                                              |     |      | S-8  |
| RISK FACTORS                                              |     |      | S-14 |
| CAPITALIZATION AND INDEBTEDNESS                           |     |      | S