Company: CIB
Filing Date: 2025-05-16
Form Type: 6-K
Source: 0001193125-25-121778
Chunk: 0

Company: Grupo Cibest S.A.
Filing Date: 2025-05-16
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

OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of May, 2025

Commission File Number 001-42656

Grupo Cibest S.A.

(Translation of registrant’s name into English)

Cra. 48 

# 26-85
Medellín, Colombia

(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 ☐

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.

|                   |     | GRUPO CIBEST S.A. 
 (Registrant)      |     |                                        |
| Date May 16. 2025 |     | By:               |     | /s/ MAURICIO BOTERO WOLFF.             |
|                   |     | Name:             |     | Mauricio Botero Wolff                  |
|                   |     | Title:            |     | Vice President of Strategy and Finance |

2

May 16, 2025 Medellín, Colombia GRUPO CIBEST S.A. ANNOUNCES MEASURES TO GUARANTEE FAIR TREATMENT OF ITS SHAREHOLDERS The following are prohibited activities directed at legal representatives, management and other employees of Grupo Cibest S.A. (“Grupo Cibest”), as well as at legal representatives, management and other employees of Fiduciaria Bancolombia S.A., the entity responsible for administering Grupo Cibest’s shares, aimed at ensuring the equitable treatment of all of Grupo Cibest’s shareholders, and which will apply to the Extraordinary General Shareholders’ Meeting:

| • |     | Encourage, promote or suggest that shareholders grant blank-check powers of attorney, where the name of the 
 representative for the shareholders’ meetings is not clearly stated.                                        |

| • |     | Receive powers of attorney from the shareholders where the name of the respective representative for the 
 shareholders’ meeting is not clearly stated.                                                             |

|