MIAX CEO Thomas Gallagher Sells ~300,000 Shares

What Happened
Thomas P. Gallagher, Chairman & CEO of Miami International Holdings, Inc. (MIAX), disposed of roughly 300,000 shares in mid‑August 2026. On 2026-08-18 he surrendered 150,300 shares to the company to satisfy tax withholding related to a restricted stock settlement (value shown ~$6.37M). On 2026-08-19 he sold 149,700 shares in the open market under a previously established Rule 10b5‑1 plan for a weighted average price of $41.13, generating approximately $6.16M. The two transactions combined represent about $12.53M in value, though only the 149,700-share trade was an open-market sale.

Key Details

• Transaction dates: 2026-08-18 (tax withholding / net settlement) and 2026-08-19 (open-market sale). Form 4 filed 2026-08-20 (timely).
• Open-market sale: 149,700 shares at weighted avg $41.13 → proceeds ~$6,157,161. Trade prices ranged $38.85–$42.56 (multiple trades; exact execution details available on request).
• Tax withholding / net settlement: 150,300 shares at $42.41 → value reported ~$6,374,223. Footnote clarifies these shares were surrendered to satisfy tax obligations and “does not represent a sale by the reporting person.”
• 10b5‑1 plan: The open-market sale was effected under a Rule 10b5‑1 plan adopted by Mr. Gallagher on December 29, 2025.
• Beneficial ownership note: Mr. Gallagher maintains beneficial and voting control through Gallagher Investments, LLC (per filing).
• Shares owned after transaction: Not specified in the provided filing excerpt.

Context

• The surrendered shares were part of tax withholding for a restricted stock award (net settlement), not an active sale decision. The separate ~149.7k‑share sale was executed under a pre‑set 10b5‑1 plan, which automates sales over time and is common for executives.
• For retail investors: purchases are typically more indicative of bullish insider sentiment; this report documents dispositions—partly administrative (tax withholding) and partly planned sales. The filing appears timely (reported within the Form 4 deadline).