Magnite, Inc.
Magnite, Inc. (MGNI) Stock Ownership
Institutional vs insider vs public ownership from 13F and float data — top holders, activity, and insider trades below.
SEC 13F · FMP · MGNI · as of Sep 30, 2025
Ownership Breakdown
352
Institutional Holders
▲ 38 vs Q2
$3.00B
Total Inst. Value
▼ $539.03M vs Q2
143.22M
Shares Outstanding
freeFloat 98.54%
138.02M
13F Shares Held
▼ 8.94M vs Q2
Institutional ownership = 13F shares ÷ total outstanding. Insider % = 100 − free float. Public % = free float − institution %. Data: FMP /symbol-positions-summary + /shares-float + SEC EDGAR.
Top Institutional Holders
MGNI largest shareholders · institutional ownership
Q3 2025 · SEC 13F
Showing top 10 holders
| Holder | Shares | % Owned | Weight | Value | Reported | Change |
|---|---|---|---|---|---|---|
FMR LLC services-computer programming, data processing, etc. | 17.14M | 12.10% | 12.10% | $373.33B | Nov 13, 2025 | ▼ 44.9K |
VANGUARD GROUP INC services-computer programming, data processing, etc. | 14.65M | 10.35% | 10.35% | $319.17B | Nov 7, 2025 | ▲ 1.09M |
BLACKROCK, INC. services-computer programming, data processing, etc. | 11.41M | 8.06% | 8.06% | $248.58B | Nov 12, 2025 | ▲ 715.1K |
CAPITAL RESEARCH GLOBAL INVESTORS services-computer programming, data processing, etc. | 6.98M | 4.93% | 4.93% | $152.09B | Nov 13, 2025 | ▼ 5.94M |
WELLINGTON MANAGEMENT GROUP LLP services-computer programming, data processing, etc. | 5.14M | 3.63% | 3.63% | $112.05B | Nov 14, 2025 | ▼ 303.3K |
AMERICAN CENTURY COMPANIES INC services-computer programming, data processing, etc. | 4.59M | 3.24% | 3.24% | $100.06B | Nov 12, 2025 | ▼ 235.1K |
BOSTON PARTNERS services-computer programming, data processing, etc. | 4.45M | 3.14% | 3.14% | $95.21B | Nov 13, 2025 | ▼ 1.13M |
GRANAHAN INVESTMENT MANAGEMENT, LLC services-computer programming, data processing, etc. | 3.87M | 2.73% | 2.73% | $84.36B | Nov 14, 2025 | ▲ 230.4K |
DIMENSIONAL FUND ADVISORS LP services-computer programming, data processing, etc. | 3.57M | 2.52% | 2.52% | $77.70B | Nov 12, 2025 | ▼ 1.33M |
GEODE CAPITAL MANAGEMENT, LLC services-computer programming, data processing, etc. | 3.40M | 2.40% | 2.40% | $74.04B | Nov 12, 2025 | ▲ 182.3K |
Data from SEC Form 13F filings. Ownership bar normalised to largest holder. Change flags: isNew / isSoldOut / changeInSharesNumber (FMP extract-analytics/holder).
Institutional Activity
Q3 2025 vs prior quarter
Q3 2025
21
Increased
+11.19M shares3
New Positions
first time holders24
Decreased
−15.28M shares0
Sold Out
fully exitedNet shares change (top 50)
4.08M
+11.19M / −15.28M
Net new holders
+0
3 new / 0 exited
Based on top 50 institutional holders by position size. Fields: isNew, isSoldOut, changeInSharesNumber (FMP extract-analytics/holder, limit=50).
Insider Buying vs Selling
MGNI insider trading · insider activity
Source: SEC Form 4
Insiders have been primarily selling shares recently. Selling may be driven by pre-scheduled Rule 10b5-1 plans rather than negative sentiment.
0
Buy transactions
8
Sell transactions
0.00
Buy/Sell ratio
$0M
Total disposed
Recent Insider Transactions
Showing 10 most recent · Common Stock only
| Name · Role | Date | Type | Shares | Price | Value | After Trans. | Filing |
|---|---|---|---|---|---|---|---|
Spillane Robert F director | May 19, 2026 | Sale | 10,000 | $13.33 | $133.3K | 43.9K | Form 4 ↗ |
BARRETT MICHAEL G. CEO | May 15, 2026 | Tax Withhold | 10,404 | $12.82 | $133.4K | 403.1K | Form 4 ↗ |
Buckley Sean Patrick President, Revenue | May 15, 2026 | Tax Withhold | 12,019 | $12.82 | $154.1K | 392.7K | Form 4 ↗ |
Evans Katie Seitz President, Operations | May 15, 2026 | Tax Withhold | 11,204 | $12.82 | $143.6K | 496.8K | Form 4 ↗ |
Day David CHIEF FINANCIAL OFFICER | May 15, 2026 | Tax Withhold | 14,170 | $12.82 | $181.7K | 493.3K | Form 4 ↗ |
Saltz Aaron CHIEF LEGAL OFFICER | May 15, 2026 | Tax Withhold | 5,627 | $12.82 | $72.1K | 270.0K | Form 4 ↗ |
Gephart Brian CHIEF ACCOUNTING OFFICER | May 15, 2026 | Tax Withhold | 3,789 | $12.82 | $48.6K | 118.6K | Form 4 ↗ |
Buonasera David CHIEF TECHNOLOGY OFFICER | May 15, 2026 | Tax Withhold | 8,335 | $12.82 | $106.9K | 294.2K | Form 4 ↗ |
Soroca Adam Lee CHIEF PRODUCT OFFICER | Feb 15, 2026 | Tax Withhold | 18,933 | $11.70 | $221.5K | 410.0K | Form 4 ↗ |
Soroca Adam Lee CHIEF PRODUCT OFFICER | Feb 18, 2026 | Sale | 21,529 | $12.00 | $258.3K | 388.4K | Form 4 ↗ |
Source: /insider-trading/search (FMP stable). Buy/Sell direction: acquisitionOrDisposition A=Buy, D=Sell. RSU vesting (M-Exempt) excluded from sentiment bar. All data from SEC EDGAR public filings.
About institutional & insider ownership
Magnite, Inc. (MGNI) is primarily owned by institutional investors, who hold approximately 96.4% of total shares outstanding. Company insiders own approximately 1.46%, while retail and public investors account for the remaining 2.17%.
The largest institutional shareholder of Magnite, Inc. is FMR LLC, holding approximately 17.14 million shares — equal to 12.10% of outstanding shares — as of September 30, 2025.
A total of 352 institutional investors currently hold MGNI stock, with a combined institutional value of approximately $3.00 billion as of the most recent 13F filing period.
Frequently asked questions
MGNI ownershipMagnite, Inc. (MGNI) is primarily owned by institutional investors, who hold approximately 96.4% of shares. The largest shareholder is FMR LLC with a 12.10% stake. Company insiders hold 1.46%. Data sourced from SEC Form 13F as of September 30, 2025.