Company: SNY
Filing Date: 2025-05-30
Form Type: 6-K
Source: 0001193125-25-131697
Chunk: 0

Company: Sanofi
Filing Date: 2025-05-30
Form: 6-K
Chunk 0
---
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 May 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 May 2025, Sanofi published the press releases attached hereto as Exhibits 99.1, 99.2 and 99.3 which are incorporated herein by reference. Exhibit Index

| Exhibit No.  
 Exhibit 99.1 
 Exhibit 99.2 |     | Description                                                                                                                          
 Press Release dated May                                                                                                              
 27, 2025: Sanofi completes acquisition of DR-0201                                                                                    
 Press Release dated May                                                                                                              
 29, 2025: Beyfortus public health advantage bolstered by first real-world comparison of infant vs maternal RSV immunization programs |
|:-------------|:----|:-------------------------------------------------------------------------------------------------------------------------------------|
| Exhibit 99.3 |     | Press Release dated May 30, 2025: Itepekimab met the primary endpoint in one of two COPD phase 3 studies                             |

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: May 30, 2025 |     |    |     | SANOFI                                   |
|:--------------------|:----|:---|:----|:-----------------------------------------|
|                     |     | By |     | /s/ Alexandra Roger                      |
|                     |     |    |     | Name: Alexandra Roger                    |
|                     |     |    |     | Title: Head of Legal Corporate & Finance |

3