[SCHEDULE 13D/A] Miami International Holdings, Inc. SEC Filing

Rhea-AI Filing Summary

Amendment No. 1 to Schedule 13D discloses updated ownership by Thomas P. Gallagher and Gallagher Investments LLC in Miami International Holdings, Inc. (MIAX) following the company's initial public offering. The Reporting Persons report beneficial ownership of 4,036,237 shares of common stock, representing 4.9% of the 80,799,866 shares outstanding as of August 26, 2025. Holdings include individually held shares, shares held by Gallagher Investments, and stock options exercisable within 60 days. Gallagher Investments surrendered 192,220 shares and $12.5 million in cash to satisfy tax withholding related to IPO-related vesting. The filing is described as a final amendment and an "exit filing" reflecting that the Reporting Persons ceased to beneficially own more than 5% as of August 26, 2025.

Positive

• Transparent disclosure of post-IPO ownership, including conversions, option holdings, and tax-related share surrender
• Lock-up agreement in place restricting sales for 180 days after the IPO, reducing near-term sell pressure
• Reporting Persons characterize holdings as long-term investment, indicating no present plans for activist actions

Negative

• Beneficial ownership fell below 5% as of August 26, 2025, reducing the formal reporting threshold that can attract investor scrutiny
• Gallagher Investments surrendered 192,220 shares and $12.5 million to satisfy tax withholding, which materially reduced the entity's share count
• Significant exercisable options (1,600,000+ aggregate) could increase beneficial ownership if exercised within 60 days

Insights

Financial Analyst

TL;DR: Ownership fell below 5% post-IPO; reported holdings include exercisable options and a mix of direct and entity holdings totaling 4,036,237 shares.

The Schedule 13D/A clarifies current beneficial ownership after the IPO conversions and post-IPO corporate actions. The aggregate 4,036,237-share position combines directly held shares, shares held by Gallagher Investments, and options exercisable within 60 days, which are relevant for potential future dilution or reclassification of voting power. The surrender of 192,220 shares plus $12.5 million to cover tax withholding materially reduced Gallagher Investments' outstanding position. The disclosure of a 180-day lock-up is standard and limits near-term disposition risk.

Corporate Governance Expert

TL;DR: CEO remains a significant insider with voting influence despite falling below the 5% reporting threshold.

The filing confirms Mr. Gallagher is Chairman and CEO and retains dispositive and voting control over Gallagher Investments, which holds a material portion of the combined stake. While the Reporting Persons state they no longer exceed 5%, Mr. Gallagher's managerial role and ownership of exercisable options mean his influence over corporate actions persists. The joint filing agreement and lock-up agreement are disclosed and consistent with standard IPO governance mechanics.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)

Miami International Holdings, Inc. (the "Issuer")

(Name of Issuer)

Common Stock, $0.001 par value per share (the "Common Stock")

(Title of Class of Securities)

59356Q108

(CUSIP Number)

Thomas P. Gallagher
c/o Miami International Holdings, Inc., 7 Roszel Road, Suite 1A
Princeton, NJ, 08540
6098977300

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

08/26/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 59356Q108

1

Name of reporting person

Thomas P. Gallagher

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF, SC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 651,101.00
8	Shared Voting Power 3,385,136.00
9	Sole Dispositive Power 651,101.00
10	Shared Dispositive Power 3,385,136.00

11

Aggregate amount beneficially owned by each reporting person

4,036,237.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.9 %

14

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13D

CUSIP No. 59356Q108

1

Name of reporting person

Gallagher Investments LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,385,136.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,385,136.00

11

Aggregate amount beneficially owned by each reporting person

3,385,136.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

4.1 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, $0.001 par value per share (the "Common Stock")
(b)	Name of Issuer: Miami International Holdings, Inc. (the "Issuer")
(c)	Address of Issuer's Principal Executive Offices: 7 Roszel Road, Suite 1A, Princeton, NEW JERSEY , 08540.
Item 1 Comment: This Amendment No. 1 ("Amendment No. 1") is being filed by the undersigned to amend the Schedule 13D filed by the Reporting Persons dated August 14, 2025 (the "Original 13D," and together with Amendment No. 1, the "Schedule 13D"). This Amendment No. 1 is the final amendment to the Schedule 13D and constitutes an "exit filing" for each of the Reporting Persons. However, as disclosed below, one or more of the Reporting Persons may become the beneficial owners of more than five percent of the Issuer's Common Stock again in the future. Except as specifically provided herein, this Amendment No. 1 does not modify any of the information previously reported on the Schedule 13D.
Item 2.	Identity and Background
(a)	This Schedule 13D is filed by the following persons (collectively, the "Reporting Persons"), pursuant to their agreement to the joint filing of this Schedule 13D attached hereto as Exhibit 1: (i) Thomas P. Gallagher, an individual resident of the State of New Jersey; and (ii) Gallagher Investments LLC, a New Jersey limited liability company
(b)	The address for each of the Reporting Persons is c/o Miami International Holdings, Inc. 7 Roszel Road, Suite 1A, Princeton, New Jersey 08540
(c)	Mr. Gallagher's principal occupation is Chairman and Chief Executive Officer of the Issuer, and the principal business of Gallagher Investments LLC ("Gallagher Investments") is holding the investments of Mr. Gallagher.
(d)	During the past five years neither of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).
(e)	During the past five years neither of the Reporting Persons was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.
(f)	United States
Item 3.	Source and Amount of Funds or Other Consideration
	Mr. Gallagher acquired the Common Stock beneficially owned by him for cash using personal funds or as compensation for serving as an executive officer, chairman and co-founder of the Issuer. On August 11, 2025, Mr. Gallagher transferred to Gallagher Investments 1,904,599 shares of Common Stock, 500 shares of Series B Preferred Stock, 135,395 shares of Nonvoting Common Stock, respectively, and options to purchase 1,536,862 shares of Nonvoting Common Stock. On August 15, 2025, (i) Gallagher Investments received 135,895 shares of the Issuer's Common Stock upon the conversion of 500 shares of Series B Preferred Stock and 135,395 shares of Nonvoting Common Stock into shares of Common Stock in connection with the Issuer's initial public offering, and (ii) Mr. Gallagher received 573,963 shares of Common Stock upon the conversion of the Issuer's Nonvoting Common Stock into shares of Common Stock in connection with the Issuer's initial public offering, in each case without consideration. On August 14, 2025, the trade date, Mr. Gallagher purchased 14,000 shares of Common Stock in the Issuer's initial public offering for $322,000 cash using personal funds. On August 26, 2025, Gallagher Investments surrendered 192,220 shares of Common Stock to the Company and $12.5 million in cash to satisfy tax withholding obligations related to restricted stock awards that vested in connection with the Issuer's initial public offering.
Item 4.	Purpose of Transaction
	The Reporting Persons acquired all of their securities for investment purposes only and are being held as a long-term investment. The Reporting Persons intend to continuously review their investment in the Issuer and may in the future determine to acquire additional securities of the Issuer or dispose of the securities of the Issuer owned by them or take any other available course of action, including surrendering or selling shares back to the Issuer for tax withholding obligations. Notwithstanding anything contained herein, the Reporting Persons specifically reserve the right to change their intention with respect to any or all of such matters. Mr. Gallagher is the Chairman and Chief Executive Officer of the Issuer and acquired his securities in that capacity. As a result, Mr. Gallagher may have influence over the corporate activities of the Issuer, including activities that may relate to items described in subparagraphs (a) through (j) of Item 4 of Schedule 13D. The Reporting Persons do not have any present plans or proposals as of the date hereof that relate to or would result in any of the transactions described in subparagraphs (a) through (j) of Item 4 of Schedule 13D.
Item 5.	Interest in Securities of the Issuer
(a)	The Reporting Persons beneficially own an aggregate of 4,036,237 shares of Common Stock as follows: (i) 573,963 shares of Common Stock held by Mr. Gallagher, (ii) 14,000 shares of Common Stock held by Mr. Gallagher jointly with his spouse, (iii) stock options exercisable for 63,138 shares of Common Stock held by Mr. Gallagher, which are exercisable within 60 days of the date hereof, (iv) 1,848,274 shares of Common Stock held by Gallagher Investments, and (v) stock options exercisable for 1,536,862 shares of Common Stock held by Gallagher Investments, which are exercisable within 60 days of the date hereof. Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments. The percentage ownership is based on 80,799,866 shares of Common Stock outstanding at the close of business on August 26, 2025.
(b)	Mr. Gallagher has the sole power to vote or to direct the vote, sole power to dispose or to direct the disposition of all shares beneficially owned by him and shares the power to vote or to direct the vote, and shares power to dispose or to direct the disposition of all shares beneficially owned by Gallagher Investments, of which Mr. Gallagher is the Manager.
(c)	Except as described under Item 3 above, the Reporting Person did not engage in any transactions in shares of the Issuer's Common Stock during the past 60 days.
(d)	Not applicable.
(e)	On August 26, 2025, the Reporting Persons ceased to be the beneficial owner of more than five percent of the Common Stock. The Reporting Persons anticipate that they may acquire beneficial ownership of additional shares of the Issuer's Common Stock in the future, and, as a result, may again own in excess of five percent of a class of the Issuer's securities. Mr. Gallagher also holds equity awards, including stock options and restricted stock awards that have not yet vested, and Mr. Gallagher may be granted additional equity awards by the Issuer in the future. As those equity awards vest, Mr. Gallagher's beneficial ownership of the Issuer's common stock may increase.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	As the Chairman and Chief Executive Officer of the Issuer, Mr. Gallagher has in the past and may receive future compensation in the form of Common Stock, options or other securities convertible into Common Stock. The Reporting Persons have entered into agreements with the underwriters of the Issuer's initial public offering pursuant to which the Reporting Persons have agreed not to sell, transfer, pledge or otherwise dispose of any of the shares of common stock for a period of 180 days after the date of the Issuer's initial public offering. There currently are no other contracts, arrangements, understandings or relationships (legal or otherwise) between the Reporting Persons and any other person with respect to any securities of the Issuer, including, but not limited to, transfer or voting of any other securities, finder's fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies. Pursuant to Rule 13d-1(k) promulgated under the Exchange Act, the Reporting Persons have entered into an agreement attached hereto as Exhibit 1, with respect to the joint filing of this Schedule 13D and any amendment or amendments hereto.
Item 7.	Material to be Filed as Exhibits.
	Exhibit 1. Joint Filing Agreement dated August 28, 2025 by the Reporting Persons Exhibit 2. Form of Lock-Up Agreement (incorporated herein by reference to Exhibit A to the Form of Underwriting Agreement, filed as Exhibit 1.1 to the Issuer's Registration Statement on Form S-1/A, filed on August 4, 2025 (File No. 333-288767)

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Thomas P. Gallagher

Signature:	Thomas P. Gallagher
Name/Title:	/s/ Thomas P. Gallagher, Individually
Date:	08/28/2025

Gallagher Investments LLC

Signature:	Gallagher Investments LLC
Name/Title:	/s/ Thomas P. Gallagher, Manager
Date:	08/28/2025

FAQ

What stake in MIAX does Thomas P. Gallagher currently report?

The Reporting Persons report beneficial ownership of 4,036,237 shares, representing 4.9% of 80,799,866 shares outstanding as of August 26, 2025.

Did Gallagher Investments sell shares after the IPO?

Gallagher Investments surrendered 192,220 shares and $12.5 million to the company to satisfy tax withholding obligations related to IPO vesting.

Are there any restrictions on selling MIAX shares held by the Reporting Persons?

Yes. The Reporting Persons entered into a 180-day lock-up agreement with the IPO underwriters prohibiting sale or transfer of shares for 180 days post-offering.

Do Mr. Gallagher or Gallagher Investments hold options?

Yes. The filing discloses options exercisable within 60 days: 63,138 for Mr. Gallagher and 1,536,862 for Gallagher Investments.

Does Mr. Gallagher retain influence over MIAX?

Yes. Mr. Gallagher is Chairman and CEO and retains dispositive and voting control over Gallagher Investments, which holds a material portion of the reported stake.