Company: SNY
Filing Date: 2025-03-06
Form Type: 6-K
Source: 0001193125-25-048070
Chunk: 0

Company: Sanofi
Filing Date: 2025-03-06
Form: 6-K
Chunk 0
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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of
March 2025

Commission File Number: 001-31368

SANOFI

(Translation of
registrant’s name into English)

46, avenue de la Grande Armée, 75017 Paris, FRANCE

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.

Form 20-F ☒ Form 40-F ☐

1

In March 2025, Sanofi published the press release attached hereto as Exhibit 99.1 which is incorporated herein by reference. Exhibit Index

2

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

| Dated: March 6 2025 |     |    |     | SANOFI                                   |
|:--------------------|:----|:---|:----|:-----------------------------------------|
|                     |     | By |     | /s/ Alexandra Roger                      |
|                     |     |    |     | Name: Alexandra Roger                    |
|                     |     |    |     | Title: Head of Legal Corporate & Finance |

3