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

_________________

FORM 8-K

_________________

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(D) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): December 2, 2025

_________________

M3-BRIGADE ACQUISITION VI CORP.

(Exact name of registrant as specified in its charter)

(212) 202-2200

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

_________________

Check the appropriate box below if the Form 8-K is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

On December 2, 2025, the board of directors (the “Board”) of M3-Brigade Acquisition VI Corp. (the “Company”) appointed Frank M. Garrison, Jr. as an independent director of the Company. Effective December 2, 2025, Mr. Garrison was appointed to the Audit and Compensation Committee of the Board.

On December 2, 2025, in connection with his appointment to the Board, Mr. Garrison entered into a letter agreement as well as an indemnity agreement with the Company.

Other than the foregoing, Mr. Garrison is not a party to any arrangement or understanding with any person pursuant to which he was appointed as director nor is he party to any transactions required to be disclosed under Item 404(a) of Regulation S-K involving the Company.

The foregoing descriptions of the letter agreement and indemnity agreement do not purport to be complete and are qualified in their entireties by reference to the letter agreement and the indemnity agreement, copies of which are attached as Exhibit 10.1 and 10.2 hereto and incorporated herein by reference.

(d)       Exhibits. The following exhibits are filed with this Form 8-K:

SIGNATURE

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