MIAX MIAMI INTERNATIONAL HOLDINGS, INC.
Executive Summary
Three mega-passive institutional investors — Vanguard, BlackRock, and Morgan Stanley — initiated new positions in MIAX totaling $105.1M during Q3 2025. This cluster likely reflects index-linked or passive rebalancing rather than a fundamental activist thesis, given the fund types and the lack of preexisting positions. The buying is unanimous in direction but limited in conviction signal because no active managers participated.
Key Financial Metrics
Institutional Positions
Net institutional flow: $105.1M
▲ Buyers (3)
| Institution | Action | Change | Position Value | Value Δ |
|---|---|---|---|---|
| Vanguard | NEW | — | $55.7M | $55.7M |
| BlackRock | NEW | — | $28.5M | $28.5M |
| Morgan Stanley | NEW | — | $21.0M | $21.0M |
Actionable Insight
The uniform passive-buying cluster signals baseline institutional acceptance and index inclusion but offers no fundamental catalyst edge. Monitor Q4 2025 13F filings for follow-through buying by active managers — that would signal a conviction-driven thesis. The recent insider selling ($1.2M over 30 days) modestly offsets the bullish positioning signal.
Key Facts
- 3 mega-passive institutions (Vanguard, BlackRock, Morgan Stanley) initiated new positions totaling $105.1M in Q3 2025
- No institutional selling was reported in the cluster
- All three buyers are passive/index fund managers, not active or activist funds
- The cluster suggests index-driven accumulation rather than a fundamental catalyst thesis
Financial Impact
$105.1M in net new institutional buying (100% passive/index-driven), representing roughly 2.7% of MIAX's $3.9B market cap
Risk Factors
- Passive flows can reverse if MIAX is removed from an index or rebalanced out
- Insider selling trend ($1.2M over 30 days) suggests insiders see limited near-term upside
- Historical calibration for score-4/5 reports on MIAX shows mixed T+20 outcomes (win rate ~50%)
Market Snapshot
Documents Analyzed
This report is based on 1 institutional 13F filing from SEC EDGAR.
| Document | Accession Number |
|---|---|
| INST-CLUSTER Data (Synthetic) | inst-cluster-MIAX-2025-Q3 |
Filters
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Jun 17, 2026
3d ago
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8-K
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 17, 2026
3d ago
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Insider Cluster
| $37.85 awaiting T+1 | awaiting T+1 | — | — |
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Jun 12, 2026
8d ago
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Insider Cluster
| $44.11 $40.24 | ▼ −8.77% | ▼ −8.18% | — |
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Jun 12, 2026
8d ago
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Insider Cluster
| $44.11 $40.24 | ▼ −8.77% | ▼ −8.18% | — |
US Market Status
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