Company: SGBAF
Filing Date: 2025-07-15
Form Type: 6-K
Source: 0001193125-25-159039
Chunk: 0

Company: SES S.A.
Filing Date: 2025-07-15
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-16of

the Securities Exchange Act of 1934

Date: July 14, 2025

Commission File Number: 333-286828

SES

(Translation of registrant’s name into English)

Château de Betzdorf

L-6815Betzdorf

Grand Duchy of Luxembourg

(Address of principal executive offices)

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

Form
20-F ☒ Form 40-F ☐

EXHIBIT INDEX The following exhibits are filed as part of this Form 6-K:

| Exhibit |     | Description   |
| 99.1    |     | Press Release |

SIGNATURE 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.

| Date: July 15, 2025 |     | SES          
 (registrant) 
 By:          |     | /s/ Thai Rubin             |
|:--------------------|:----|:-------------|:----|:---------------------------|
|                     |     |              |     | Name: Thai Rubin           |
|                     |     |              |     | Title: Chief Legal Officer |