Thomas P. Gallagher - 03 Sep 2026 Form 4 Insider Report for MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX)

Reporting relationship: Chairman & CEO, Director
Issuer ticker: MIAX
Reported as of: 03 Sep 2026
Net transaction value: -$1,994,210
SEC form: 4
Accepted by SEC: 04 Sep 2026, 16:35:00 UTC
Prior SEC filing: 20 Aug 2026
Source filing: View source filing
Reporting owner signature: /s/Alessandra Maria Corona Henriques, Attorney-in-Fact

Key filing fact

Thomas P. Gallagher filed Form 4 for MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX) on 04 Sep 2026.

Key facts

This page summarizes Thomas P. Gallagher's Form 4 filing for MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX).
11 reported transactions and 5 derivative rows are listed below.
Accepted by SEC: 04 Sep 2026, 16:35.

Change

Previous filing in this sequence was filed on 20 Aug 2026.
Current net transaction value: -$1,994,210.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0002080477 Primary reporting owner

Gallagher Thomas P.

Relationship: Chairman & CEO, Director
Address: C/O MIAMI INTERNATIONAL HOLDINGS, INC, 7 ROSZEL ROAD, SUITE 1A, PRINCETON
Signature: /s/Alessandra Maria Corona Henriques, Attorney-in-Fact
Signature date: 04 Sep 2026

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

MIAX transaction

Common Stock

Options Exercise

Transaction value
Shares: +47,000
Change %: +3.3%
Price: $12.00^*
Shares after: 1,470,275
Date: 03 Sep 2026
Ownership: By Gallagher Investments, LLC
Footnotes: F1, F2

MIAX transaction

Common Stock

Sale

Transaction value: $1,994,210
Shares: -47,000
Change %: -3.2%
Price: $42.43
Shares after: 1,423,275
Date: 03 Sep 2026
Ownership: By Gallagher Investments, LLC
Footnotes: F1, F2, F3

MIAX transaction

Common Stock

Options Exercise

Transaction value
Shares: +16,666
Change %: +2.2%
Price: $12.00^*
Shares after: 760,605
Date: 03 Sep 2026
Ownership: Direct

MIAX transaction

Common Stock

Options Exercise

Transaction value
Shares: +8,333
Change %: +1.1%
Price: $12.00^*
Shares after: 768,938
Date: 03 Sep 2026
Ownership: Direct

MIAX transaction

Common Stock

Options Exercise

Transaction value
Shares: +13,140
Change %: +1.7%
Price: $15.22^*
Shares after: 782,078
Date: 03 Sep 2026
Ownership: Direct

MIAX transaction

Common Stock

Options Exercise

Transaction value
Shares: +4,464
Change %: +0.57%
Price: $22.40^*
Shares after: 786,542
Date: 03 Sep 2026
Ownership: Direct

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

MIAX transaction Derivative

Nonqualified Stock Option (Right to Buy)

Options Exercise

Transaction value
Shares: -47,000
Change %: -20%
Price: $0.000000^*
Shares after: 188,000
Date: 03 Sep 2026
Ownership: By Gallagher Investments, LLC
Underlying class: Common Stock
Underlying amount: 47,000
Exercise price: $12.00
Footnotes: F1, F2, F4

MIAX transaction Derivative

Incentive Stock Option (Right to Buy)

Options Exercise

Transaction value
Shares: -16,666
Change %: -100%
Price: $0.000000^*
Shares after: 0
Date: 03 Sep 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 16,666
Exercise price: $12.00
Footnotes: F4

MIAX transaction Derivative

Incentive Stock Option (Right to Buy)

Options Exercise

Transaction value
Shares: -8,333
Change %: -100%
Price: $0.000000^*
Shares after: 0
Date: 03 Sep 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 8,333
Exercise price: $12.00
Footnotes: F4

MIAX transaction Derivative

Incentive Stock Option (Right to Buy)

Options Exercise

Transaction value
Shares: -13,140
Change %: -100%
Price: $0.000000^*
Shares after: 0
Date: 03 Sep 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 13,140
Exercise price: $15.22
Footnotes: F4

MIAX transaction Derivative

Incentive Stock Option (Right to Buy)

Options Exercise

Transaction value
Shares: -4,464
Change %: -33%
Price: $0.000000^*
Shares after: 8,928
Date: 03 Sep 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 4,464
Exercise price: $22.40
Footnotes: F5

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 5 footnotes

Footnote F1

This transaction was effected pursuant to a previously established Rule 10b5-1 Plan adopted by the Reporting Person on December 29, 2025.

Footnote F2

Mr. Gallagher maintains beneficial ownership, including dispositive and voting control, over Gallagher Investments, LLC.

Footnote F3

This transaction was executed in multiple trades throughout the day at prices ranging from $42.00 to $42.68. The price reported above reflects the weighted average sales price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the Issuer or a security holder of the Issuer, full information regarding the number of shares and prices at which the transaction was effected.

Footnote F4

The options are fully vested.

Footnote F5

4,464 of the shares subject to this incentive stock option are vested. 4,464 shares subject to this incentive stock option will vest on June 16, 2027 and the remaining 4,464 shares subject to this incentive stock option will vest on June 16, 2028, subject to the Reporting Person's continued service to the Issuer or its subsidiaries through the applicable vesting date.