Company: SNY
Filing Date: 2025-03-21
Form Type: S-8 POS
Source: 0001193125-25-059686
Chunk: 0

Company: Sanofi
Filing Date: 2025-03-21
Form: S-8 POS
Chunk 0
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As filed with the Securities and Exchange Commission on March 21, 2025 Registration No. 333-278502 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 SANOFI (Exact name of Registrant as specified in its charter)

| Republic of France              |     | Not Applicable        |
| (State or other jurisdiction of 
 incorporation or organization)  |     | -I.R.S. Employer      
 Identification Number |

46, avenue de la Grande Armée, 75017 Paris, France (Address of Registrant’s principal executive offices) ACTION 2024 SHAREHOLDING PLAN (Full title of the plan) Debora C. Pellicano Chief Financial Officer North America & Head of Finance Specialty Care Sanofi U.S. Services Inc. 450 Water Street Cambridge, Massachusetts 02141 Tel. No. +1 (908) 981-5000 (Name, address and telephone number of agent for service) Copies to: Sami Toutounji, Esq. Gide Loyrette Nouel LLP One Rockefeller Plaza Suite 3040, New York, NY 10020 (212) 403-6700 Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-acceleratedfiler, a smaller reporting company or an emerging growth company. See definitions of “large accelerated filer,” “accelerated filer,” “small reporting company,” and “emerging growth company” in Rule 12b-2of the Exchange Act.

| Large accelerated filer |     | ☒ |     | Accelerated filer         |     | ☐ |
| Non-accelerated filer   |     | ☐ |     | Smaller reporting company |     | ☐ |
|                         |     |   |     | Emerging growth company   |     | ☐ |

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

EXPLANATORY NOTE: DEREGISTRATION OF SECURITIES

This Post-Effective Amendment No. 1 to the Registration Statement on Form S-8, Registration
No. 333-