Thomas P. Gallagher - 18 Aug 2026 Form 4 Insider Report for MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX)

Reporting relationship: Chairman & CEO, Director
Issuer ticker: MIAX
Reported as of: 18 Aug 2026
Net transaction value: -$6,157,161
SEC form: 4
Accepted by SEC: 20 Aug 2026, 16:12:06 UTC
Prior SEC filing: 06 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 20 Aug 2026.

Key facts

This page summarizes Thomas P. Gallagher's Form 4 filing for MIAMI INTERNATIONAL HOLDINGS, INC. (MIAX).
2 reported transactions and 0 derivative rows are listed below.
Accepted by SEC: 20 Aug 2026, 16:12.

Change

Previous filing in this sequence was filed on 06 Aug 2026.
Current net transaction value: -$6,157,161.

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: 20 Aug 2026

Reported non-derivative transactions

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

MIAX transaction

Common Stock

Tax liability

Transaction value
Shares: -150,300
Change %: -8.7%
Price: $42.41^*
Shares after: 1,572,975
Date: 18 Aug 2026
Ownership: By Gallagher Investments, LLC
Footnotes: F1, F2

MIAX transaction

Common Stock

Sale

Transaction value: $6,157,161
Shares: -149,700
Change %: -9.5%
Price: $41.13
Shares after: 1,423,275
Date: 19 Aug 2026
Ownership: By Gallagher Investments, LLC
Footnotes: F2, F3, F4

^* 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 4 footnotes

Footnote F1

Represents shares that have been surrendered to the Company to satisfy tax withholding and remittance obligations in connection with the net settlement of restricted stock awards and does not represent a sale by the reporting person.

Footnote F2

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

Footnote F3

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

Footnote F4

This transaction was executed in multiple trades throughout the day at prices ranging from $38.85 to $42.56. 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.