M3-Brigade Acquisition VI Corp.

As filed with the Securities and Exchange Commission on August 4, 2025.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Exact name of registrant as specified in its charter)

1700 Broadway – 19 th Floor

New York, NY 10019

(212) 202-2200

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Executive Chairman of the Board of Directors

1700 Broadway – 19 th Floor

New York, NY 10019

(212) 202-2200

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box.☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.☐

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 7(a)(2)(B) of the Securities Act.

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted

Subject to Completion, dated , 2025

PRELIMINARY PROSPECTUS

$300,000,000

30,000,000 Units

M3-Brigade Acquisition VI Corp. is a blank check company incorporated as a Cayman Islands exempted company for the purpose of effecting a merger, share exchange, asset acquisition, share purchase, reorganization or similar business combination with one or more businesses, which we refer to as our initial business combination. We have not selected any specific business combination target and we have not, nor has anyone on our behalf, engaged in any substantive discussions, directly or indirectly, with any business combination target with respect to an initial business combination with us. However, members of our management team had been actively in discussions with potential business combination partners in their capacity as officers and directors of the Prior SPACs (as defined herein) and, although we do not currently expect to do so, we may pursue business combination partners that had previously been in discussions with the Prior SPACs’ respective management teams.

This is an initial public offering of our securities. Each unit has an offering price of $10.00 and consists of one Class A ordinary share and one-third of one redeemable warrant. Each whole warrant entitles the holder thereof to purchase one Class A ordinary share at a price of $11.50 per share, subject to adjustment as described herein. Only whole warrants are exercisable. No fractional warrants will be issued upon separation of the units and only whole warrants will trade. The warrants will become exercisable 30 days after the completion of our initial business combination, and will expire five years after the completion of our initial business combination or earlier upon redemption or our liquidation, as described herein. The underwriters have a 45-day option from the date of this prospectus to purchase up to an additional 4,500,000 units to cover over-allotments, if any.

We will provide our public shareholders with the opportunity to redeem all or a portion of their Class A ordinary shares that were sold as part of the units in this offering, which we refer to collectively as our public shares, upon the completion of our initial business combination at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the trust account described below as of two business days prior to the consummation of our initial business combination, including interest earned on the funds held in the trust account, less taxes payable, divided by the number of then outstanding public shares, subject to the limitations and on the conditions described herein. Notwithstanding the foregoing redemption rights, our amended and restated memorandum and articles of association provide that a public shareholder, together with any affiliate of such shareholder or any other person with whom such shareholder is acting in concert or as a “group” (as defined under Section 13 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)), may be restricted from redeeming its shares with respect to more than an aggregate of 15% of the shares sold in this offering without our prior consent. See “Summary — The Offering — Limitation on redemption rights of shareholders holding 15% or more of the shares sold in this offering if we hold shareholder vote” for further discussion on certain limitations on redemption rights.

M3-Brigade Sponsor VI LLC (our “sponsor”) and Cantor Fitzgerald & Co., the representative of the underwriters, have committed to purchase an aggregate of 5,333,333 private placement warrants, each exercisable to purchase one Class A ordinary share at$11.50 per share, subject to adjustment, at a price of$1.50 per warrant, or$8,000,000 in the aggregate in a private placement that will close simultaneously with the closing of this offering. Each private placement warrant is exercisable to purchase one Class A ordinary share at$11.50 per share.

Of those 5,333,333 private placement warrants, the sponsor has agreed to purchase 4,333,333 private placement warrants and Cantor Fitzgerald & Co. has agreed to purchase 1,000,000 private placement warrants. Twenty-one institutional investors (none of which are affiliated with any member of our management, our sponsor or any other investor), which we refer to as the “non-managing sponsor investors” throughout this prospectus, have expressed an interest to purchase, indirectly through the purchase of non-managing sponsor membership interests, an aggregate of 4,000,000 private placement warrants at a price of$1.50 per warrant ($6,000,000 in the aggregate) in a private placement that will close simultaneously with the closing of this offering. Subject to each non-managing sponsor investor purchasing, through the sponsor, the private placement warrants allocated to it in connection with the closing of this offering, the sponsor will issue membership interests at a nominal purchase price to the non-managing sponsor investors reflecting interests in an aggregate of 3,000,000 founder shares held by the sponsor. Membership interests reflecting interests in the remaining 5,625,000 founder shares held by the sponsor will be held by the Sponsor Manager (as defined herein) and our directors.

The interests of the members of the sponsor are denominated in two classes of membership interest units: (i) class A membership units representing interests in the founder shares and (ii) class B membership units that will represent an interest in the private placement warrants. All members of the sponsor, including the Sponsor Manager and any non-managing sponsor investor that may join the sponsor concurrently with this offering will hold both classes of membership units representing their proportional interest in the founder shares and private placement warrants. Pursuant to an agreement of all members of the sponsor, the management and control of the sponsor is vested exclusively with the Sponsor Manager, without any voting, veto, consent or other participation rights by any non-managing sponsor investors regardless of their unit ownership. As a result of this management structure, non-managing sponsor investors will have no right to control the sponsor, or participate in any decision regarding the disposal of any security held by the sponsor, or otherwise.

None of the non-managing sponsor investors have expressed to us an interest in purchasing any of the units in this offering and neither us nor the representative has had discussions with any non-managing sponsor investors regarding any purchases of units in this offering. Any potential purchase of the non-managing sponsor membership interests would not be contingent upon the participation in this offering or vice-versa. If the non-managing sponsor investors purchase units in the offering, and depending on how many units are purchased by the non-managing sponsor investors, the post-offering trading volume, volatility and liquidity of our securities may be reduced relative to what they would have been had the units been more widely sold to other public investors. We do not expect any potential purchases of units by non-managing sponsor investors to negatively impact our ability to meet Nasdaq listing eligibility requirements. In addition, the underwriters have full discretion to allocate the units to investors and may determine not to sell any units to the non-managing sponsor investors, and in no case would any of the non-managing sponsor investors be sold more than 9.9% of the units to be sold in this offering. The underwriters would receive the same upfront discounts and commissions and deferred underwriting commissions on units purchased by the non managing sponsor investors, if any, as it will on the other units sold to the public in this offering. In addition, if the non-managing sponsor investors purchase units in the offering, the non-managing sponsor investors would not have any obligation to vote any of their public shares in favor of our initial business combination. Nevertheless, the non-managing sponsor investors would be incentivized to vote any of their public shares, if any, in favor of a business combination due to their indirect ownership through the sponsor of founder shares and private placement warrants. For a discussion of certain additional arrangements with the non-managing sponsor investors, see “Summary — The Offering — Founder Shares.”

On June 6, 2025, our sponsor paid $25,000, or approximately $0.003 per share, to cover certain of our offering costs in exchange for 8,625,000 Class B ordinary shares, up to 1,125,000 of which will be surrendered to us for no consideration after the closing of this offering depending on the extent to which the underwriters’ over-allotment option is exercised, which will automatically convert into Class A ordinary shares in connection with the consummation of our initial business combination, or earlier at the option of the holders thereof on a one-for-one basis, subject to the adjustments described herein. If we increase or decrease the size of the offering pursuant to Rule 462(b) under the Securities Act, we will effect a share capitalization or a share repurchase or redemption or other appropriate mechanism, as applicable, with respect to our Class B ordinary shares immediately prior to the consummation of the offering in such amount as to maintain the ownership of founder shares by our initial shareholders, on an as-converted basis, at 20% of our issued and outstanding ordinary shares upon the consummation of this offering. Prior to and/or in connection with the closing of our initial business combination, only holders of our Class B ordinary shares will be entitled to vote on the appointment and removal of directors or continuing the company in a jurisdiction outside the Cayman Islands (including any special resolution required to amend the constitutional documents of the company or to adopt new constitutional documents of the company, in each case, as a result of the company approving a transfer by way of continuation in a jurisdiction outside the Cayman Islands). On any other matters submitted to a vote of our shareholders prior to or in connection with the completion of our initial business combination, holders of the Class B ordinary shares and holders of the Class A ordinary shares will vote together as a single class, except as required by law. Upon consummation of this offering, we will repay up to $300,000 in loans made to us by our sponsor to cover offering-related and organizational expenses. In the event that we obtain working capital loans from our sponsor to finance transaction costs related to our initial business combination, up to $1,500,000 of such loans may be convertible into up to an additional 1,500,000 private placement warrants, at the price of $1.50 per warrant. See “Summary — The Offering — Founder Shares,” “Summary — The Offering — Transfer Restrictions on Founder Shares,” “Summary — The Offering — Founder Shares Conversion and Anti-Dilution Rights,” “Summary — Sponsor Information” and “Description of Securities — Founder Shares” for further discussion on our sponsor’s and our affiliates’ securities.

Of the proceeds we receive from this offering and the sale of the private placement warrants described in this prospectus, $300,000,000, or $345,000,000 if the underwriters’ over-allotment option is exercised in full ($10.00 per unit in either case), will be deposited into a trust account located in the United States with Continental Stock Transfer & Trust Company acting as trustee and held as cash or invested only in (i) U.S. government treasury obligations with a maturity of 185 days or less or in money market funds meeting certain conditions under Rule 2a-7 under the Investment Company Act which invest only in direct U.S. government treasury obligations or (ii) an interest bearing bank demand deposit account or other accounts at a bank. Except with respect to interest earned on the funds held in the trust account that may be released to us to pay our taxes, if any, the proceeds from this offering and the sale of the private placement warrants will not be released from the trust account until the earliest of (i) the completion of our initial business combination, (ii) the redemption of our public shares if we are unable to complete our initial business combination within the completion window, subject to applicable law, or (iii) the redemption of our public shares properly submitted in connection with a shareholder vote to amend our amended and restated memorandum and articles of association to (A) modify the substance or timing of our obligation to allow redemption in connection with our initial business combination or to redeem 100% of our public shares if we have not consummated an initial business combination within the completion window or (B) with respect to any other material provisions relating to shareholders’ rights or pre-initial business combination activity. The proceeds deposited in the trust account could become subject to the claims of our creditors, if any, which could have priority over the claims of our public shareholders. The proceeds placed in the trust account and the interest earned thereon shall not be used to pay for possible excise tax or any other fees or taxes that may be levied on the Company on any redemptions or stock buybacks by the Company pursuant to any current, pending or future rules or laws, including without limitation any excise tax due under the Inflation Reduction Act of 2022.

We have until the date that is 24 months from the closing of this offering or until such earlier liquidation date as our board of directors may approve, to consummate our initial business combination. If we anticipate that we may be unable to consummate our initial business combination within such 24-month period, we may seek shareholder approval to amend our amended and restated memorandum and articles of association to extend the date by which we must consummate our initial business combination. If we seek shareholder approval for an extension, holders of Class A ordinary shares will be offered an opportunity to redeem their shares at a per share price, payable in cash, equal to the aggregate amount then on deposit in the trust account, including interest earned thereon (less taxes payable), divided by the number of then issued and outstanding Class A ordinary shares, subject to applicable law. The redemption rights will also include the requirement that any beneficial owner on whose behalf a redemption right is being exercised must identify itself in order to validly redeem its shares. If we are unable to complete our initial business combination within the completion window, we will redeem 100% of the Class A ordinary shares at a per share price, payable in cash, equal to the aggregate amount then on deposit in the trust account, including interest earned thereon (less taxes payable and up to $100,000 of interest income to pay dissolution expenses), divided by the number of then issued and outstanding Class A ordinary shares, which redemption will constitute full and complete payment for the public shares and completely extinguish public shareholders’ rights as shareholders (including the right to receive further liquidation or other distributions, if any), subject to our obligations under Cayman Islands law to provide for claims of creditors and subject to the other requirements of applicable law.

Currently, there is no public market for our units, Class A ordinary shares or warrants. We intend to apply to have to list our units listed on The Nasdaq Global Market, or Nasdaq, under the symbol “MBVIU” on or promptly after the date of this prospectus. We cannot guarantee that our securities will be approved for listing on Nasdaq. We expect the Class A ordinary shares and warrants comprising the units to begin separate trading on the 52 nd day following the date of this prospectus unless Cantor Fitzgerald & Co., the representative of the underwriters, informs us of its decision to allow earlier separate trading, subject to our satisfaction of certain conditions as described further herein. Once the securities comprising the units begin separate trading, we expect that the Class A ordinary shares and the warrants will be listed on Nasdaq under the symbols “MBVI” and “MBVIW”, respectively.

We are an “emerging growth company” and a “smaller reporting company” under applicable federal securities laws and will be subject to reduced public company reporting requirements. Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page 50 for a discussion of information that should be considered in connection with an investment in our securities. Investors will not be entitled to protections normally afforded to investors in Rule 419 blank check offerings.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

(1) Includes $0.20 per unit (excluding any units sold pursuant to the underwriters’ option to purchase additional units), or $6,000,000 in the aggregate (whether or not the underwriters’ option to purchase additional units is exercised), payable to Cantor Fitzgerald & Co. upon the closing of this offering. Also includes $0.45 per unit on units other than those sold pursuant to the underwriters’ option to purchase additional units and $0.65 per unit on units sold pursuant to the underwriters’ option to purchase additional units, or $13,500,000 in the aggregate or up to $16,425,000 in the aggregate if the underwriters’ over-allotment option is exercised in full, payable to Cantor Fitzgerald & Co. for deferred underwriting commissions to be deposited into a trust account located in the United States and released to Cantor Fitzgerald & Co. for its own account only upon the completion of an initial business combination. See also “Underwriting” for a description of compensation and other items of value payable to the underwriters.

Of the proceeds we receive from this offering and the sale of the private placement warrants described in this prospectus, $300 million, or $345 million if the underwriter’s overallotment option is exercised in full ($10.00 per unit in either case), will be placed into a U.S.-based trust account with Continental Stock Transfer & Trust Company acting as trustee.

Because our sponsor acquired the founder shares at a nominal price, our public shareholders will incur an immediate and substantial dilution upon the closing of this offering, assuming no value is ascribed to the warrants included in the units. Further, the Class A ordinary shares issuable in connection with the conversion of the founder shares may result in material dilution to our public shareholders due to the anti-dilution rights of our founder shares that may result in an issuance of Class A ordinary shares on a greater than one-to-one basis upon conversion. If we raise additional funds through equity or convertible debt issuances, our public shareholders may also suffer significant dilution. This dilution would increase to the extent that the anti-dilution provision of the founder shares results in the issuance of Class A shares on a greater than one-to-one basis upon conversion of the founder shares at the time of our initial business combination. The compensation to be paid to the sponsor, Class A ordinary shares issuable in connection with the conversion of the founder shares, and securities to be issued to the sponsor in the private placement may result in a material dilution of our public shareholders’ equity interests. Our public shareholders may also experience material dilution from the exercise of the private placement warrants to be purchased simultaneously with the closing of this offering, which private placement warrants may be exercised on a cashless basis along with the public warrants under the circumstances specified in the warrant agreement. Additionally, our public shareholders may experience material dilution if the $1,500,000 in working capital loans is advanced by our sponsor and our sponsor elects to convert the working capital loans into up to an additional 1,500,000 private placement warrants, which private placement warrants may result in material dilution to our public shareholders if exercised on a cashless basis. See “Risk Factors — Risks Relating to our Securities — The nominal purchase price paid by our sponsor for the founder shares may result in significant dilution to the implied value of your public shares upon the consummation of our initial business combination, and our sponsor is likely to make a substantial profit on its investment in us in the event we consummate an initial business combination, even if the business combination causes the trading price of our ordinary shares to materially decline”, “— We may issue additional Class A ordinary shares or preference shares to complete our initial business combination or under an employee incentive plan after completion of our initial business combination. We may also issue Class A ordinary shares upon the conversion of the Class B ordinary shares at a ratio greater than one-to-one in connection with our initial business combination as a result of the anti-dilution provisions contained in our amended and restated memorandum and articles of association. Any such issuances would dilute the interest of our shareholders and likely present other risks”, “— The value of the founder shares following completion of our initial business combination is likely to be substantially higher than the nominal price paid for them, even if the trading price of our ordinary shares at such time is substantially less than $10.00 per share”and “Dilution.”

The following table illustrates the difference between the public offering price per unit and our net tangible book value per share (“NTBV”), as adjusted to give effect to this offering and assuming the redemption of our public shares at varying levels and the exercise in full and no exercise of the over-allotment option. See “Dilution.”

As more fully discussed in “Management — Conflicts of Interest,” our sponsor, members of our management team and directors will directly or indirectly own our securities following this offering, and accordingly, they may have a conflict of interest in determining whether a particular target business is an appropriate business with which to effectuate our initial business combination. The low price that our sponsor, paid for the founder shares creates an incentive whereby members of our management team and our directors could potentially make a substantial profit even if we select an acquisition target that subsequently declines in value and is unprofitable for public shareholders. Our initial shareholders will purchase private placements warrants in a transaction that will close simultaneously with the closing of this offering. If we do not complete our initial business combination within the prescribed time frame, the private placement warrants will expire worthless. Additionally, each of our officers and directors presently has, and any of them in the future may have additional, fiduciary, contractual or other obligations or duties to one or more other entities pursuant to which such officer or director is or will be required to present a business combination opportunity to such entities. None of our officers or directors shall have a duty to present any potential business combination opportunity to the Company. As a result, there may be actual or potential material conflicts of interest between our sponsor and its affiliates, including M3 Partners and Brigade, on one hand, and purchasers in this offering on the other. Our sponsor and our officers and directors may sponsor or form other special purpose acquisition companies similar to ours or may pursue other business or investment ventures during the period in which we are seeking an initial business combination. Furthermore, if we are unable to complete our initial business combination within the completion window (as defined herein), the founder shares and private placement warrants may expire worthless, except to the extent they receive liquidating distributions from assets outside the trust account, which could create an incentive for our sponsor, executive officers and directors to complete a transaction even if we select an acquisition target that subsequently declines in value and is unprofitable for public shareholders. Further, each of our officers and directors may have a conflict of interest with respect to evaluating a particular business combination if the retention or resignation of any such officers and directors was included by a target business as a condition to any agreement with respect to our initial business combination. See “Summary — Sponsor Information”, “Summary — The Offering — Conflicts of Interest”, “Proposed Business — Sourcing of Potential Business Combination Targets” and “Management — Conflicts of Interest” for more information.

The underwriters are offering the units for sale on a firm commitment basis. The underwriters expect to deliver the units to the purchasers on or about , 2025.

Sole Book-Running Manager

Cantor

, 2025