UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER
PURSUANT TO RULE 13a-16 OR 15d-16
UNDER THE SECURITIES EXCHANGE ACT OF 1934

Date of Report: September 11, 2025

Commission File Number: 001-39570

TIM S.A.
(Exact name of Registrant as specified in its Charter)

João Cabral de Melo Neto Avenue, 850 – North Tower – 12^th floor
22775-057 Rio de Janeiro, RJ, Brazil
(Address of principal executive office)

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 ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1).

Yes ☐ No ☒

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7).

Yes ☐ No ☒

TIM S.A.

Publicly-Held Company

CNPJ/MF 02.421.421/0001-11

NIRE 333.0032463-1

MINUTES OF THE BOARD OF DIRECTORS’ MEETING

HELD ON SEPTEMBER 8^TH, 2025

DATE, TIME AND PLACE: September 8^th, 2025, at 10.00 a.m., at the head office of TIM S.A. (“Company”), domiciled at Avenida João Cabral de Mello Neto, 850, Torre Sul, 13° floor, Barra da Tijuca, in the city and State of Rio de Janeiro.

PRESENCE: The Board of Directors’ Meeting of the Company was held at the date, time and place mentioned above, with the presence of Messrs. Nicandro Durante, Adrian Calaza, Alberto Mario Griselli, Alessandra Michelini, Claudio Giovanni Ezio Ongaro, Gigliola Bonino, Herculano Aníbal Alves and Leonardo de Carvalho Capdeville, either in person or by means of audio or videoconference, as provided in the 2^nd paragraph of Section 25, of the Company’s By-laws. Justified absence of Messrs. Flavia Maria Bittencourt and Gesner José de Oliveira Filho.

BOARD: Mr. Nicandro Durante – Chairman; and Mrs. Fabiane Reschke – Secretary.

AGENDA: To resolve on the agreements related to the Company's energy self-production project.

RESOLUTIONS: Upon the review of the material presented and filed at the Company’s head office, and based on the information provided and discussions of the subject included on the Agenda, the Board Members, unanimously by those present and with the abstention of the legally restricted, decided to register the discussions as follows:

Further to the discussions and analyses held at this Board’s meeting on February 24^th, 2025, and after the amendment of the Company's Bylaws, approved at the Extraordinary General Meeting held on March 27^th, 2025, the Board Members approved the execution of any instruments, contracts, and terms related to the Company's energy self-production project, including the execution of a consortium agreement to formalize the legal structure for the execution of said project, in the terms and conditions of the support material presented, as well as authorized the Company's Officers and/or attorneys to adopt all measures necessary for the faithful compliance with this resolution, in the terms and conditions of the support material presented.

CONT. OF MINUTES OF THE BOARD OF DIRECTORS’ MEETING OF TIM S.A.

September 8^th, 2025

CLOSING: With no further issues to discuss, the meeting was adjourned, and these minutes drafted as summary, read, approved and signed by all attendees Board Members.

I herein certify that these minutes are the faithful copy of the original version duly recorded in the respective corporate book.

Rio de Janeiro (RJ), September 8^th, 2025.

FABIANE RESCHKE

Secretary

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.