Company: SNY
Filing Date: 2025-10-29
Form Type: 424B5
Source: 0001193125-25-255563
Chunk: 126

Company: Sanofi
Filing Date: 2025-10-29
Form: 424B5
Chunk 126
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 cannot be sure as to the liquidity of or the existence of trading markets for any debt securities offered. In the event that we do not list debt securities of any series on a U.S. national securities exchange, various broker-dealers may make a market in the debt securities, but will have no obligation to do so, and may discontinue any market making at any time without notice. Consequently, it may be the case that no broker-dealer will make a market in debt securities of any series or that the liquidity of the trading market for the debt securities will be limited. Expenses The expenses of any offering of debt securities will be detailed in the relevant prospectus supplement. 39

VALIDITY OF SECURITIES

The validity of the debt securities offered hereby will be passed upon by Jones Day, French and U.S. counsel for Sanofi. Certain matters of
French law and New York law will be passed upon for any underwriters or agents by any law firm named in the applicable prospectus supplement.

EXPERTS

The consolidated financial statements of Sanofi and its subsidiaries incorporated in this Prospectus by reference from the 2023 Form 20-F, and the effectiveness of Sanofi and its subsidiaries’ internal control over financial reporting as of December 31, 2023 have been audited by Ernst & Young et Autres and
PricewaterhouseCoopers Audit, independent registered public accounting firms, as stated in their reports, which are incorporated herein by reference. Such consolidated financial statements and management’s assessment of the effectiveness of
internal control over financial reporting as of December 31, 2023 have been so incorporated in reliance upon the reports of such firms given on the authority of such firms as experts in accounting and auditing.

40

$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 Prospectus Supplement Global Coordinators and Joint Book-Running Managers

| Barclays |     | BNP Paribas |     | BofASecurities |

Joint Book-Running Managers

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

October 27, 2025