Company: SNY
Filing Date: 2025-10-29
Form Type: 424B5
Source: 0001193125-25-255563
Chunk: 8

Company: Sanofi
Filing Date: 2025-10-29
Form: 424B5
Chunk 8
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.1 of National Instrument 45-106 Prospectus Exemptions (“NI 45-106”) or, in Ontario, as such term is defined in
section 73.3(1) of the Securities Act (Ontario); and (iii) is a “permitted client” as such term is defined in section 1.1 of National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations.

Rescission Rights and Remedies

Securities legislation in certain of the Canadian jurisdictions provides certain purchasers of securities, with a remedy for damages or
rescission, or both, in addition to any other rights they may have at law, if this prospectus (including any amendment thereto) contains a “misrepresentation” as defined under applicable Canadian securities laws. These remedies, or
notice with respect to these remedies, must be exercised or delivered, as the case may be, by the purchaser within the time limits prescribed under, and are subject to limitations and defenses under, applicable Canadian securities legislation. The
purchaser should refer to the applicable Canadian securities legislation or consult with a legal advisor.

S-3

INCORPORATION OF INFORMATION WE FILE WITH THE SEC We have filed with the U.S. Securities and Exchange Commission (the “SEC”) a registration statement on Form F-3relating to the notes covered by this prospectus supplement and the attached prospectus. This prospectus supplement and the attached prospectus are part of that registration statement and do not contain all the information in the registration statement. Whenever a reference is made in this prospectus supplement and the attached prospectus to a contract or other document of Sanofi, the reference is only a summary. You should refer to the exhibits that are a part of the registration statement for a copy of the contract or other document. You may review a copy of the registration statement at the SEC’s public reference room in Washington, D.C., as well as through the SEC’s Internet site at http://www.sec.gov. The SEC allows us to incorporate by reference the information we file with them, which means that:

| • |     | incorporated documents are considered part of this prospectus supplement and the attached prospectus; |

| • |     | we can disclose important information to you by referring to those documents; and |

| • |     | information that we file with the SEC in the future and incorporate by reference herein will automatically update                                            
 and supersede information in this prospectus supplement and the attached prospectus