Mar 31, 2026 filings. Quarterly 13F reports arrive up to 45 days after quarter end; this register is filed through May 29, 2026.
286 institutional managers reported holding MGNI for the quarter ended Mar 31, 2026. Together they hold about 88% of shares outstanding; the top 10 hold 45%. 42 opened new positions; 59 closed out. Complete ranked register from SEC 13F filings.
| manager | shares | % out | value (Mar 31, 2026 close) | change | held since |
|---|---|---|---|---|---|
| Vanguard Group | 15.14M | 10.23% | $179.8M | added +2.3% | 2020 Q3 |
| BlackRock | 11.66M | 7.87% | $138.4M | added +0.6% | 2020 Q3 |
| Wellington Management | 9.19M | 6.21% | $109.1M | added +6.5% | 2022 Q3 |
| Capital Research Global Investors | 5.02M | 3.39% | $59.6M | trimmed -61.1% | 2024 Q4 |
| Boston Partners | 4.72M | 3.19% | $56.0M | added +14.9% | 2024 Q2 |
| American Century Companies INC | 4.63M | 3.13% | $54.9M | trimmed -12.5% | 2022 Q4 |
| FMR (Fidelity) | 4.51M | 3.04% | $53.5M | trimmed -32.7% | 2020 Q4 |
| Dimensional Fund Advisors | 3.98M | 2.69% | $47.3M | added +10.2% | 2020 Q3 |
| Nuveen | 3.59M | 2.42% | $42.6M | added +1.7% | 2020 Q3 |
| Geode Capital | 3.55M | 2.40% | $42.2M | added +3.5% | 2020 Q3 |
| Nine Ten Capital Management LLC (focused) | 3.48M | 2.35% | $41.3M | added +15.9% | 2020 Q2 |
| State Street | 3.16M | 2.14% | $37.5M | added +0.7% | 2020 Q3 |
| Edenbrook Capital, LLC (focused) | 2.80M | 1.89% | $33.2M | unchanged | 2020 Q3 |
| Granahan Investment Management, LLC | 2.55M | 1.72% | $30.3M | trimmed -18.1% | 2020 Q2 |
| Ophir Asset Management Pty LTD (focused) | 2.12M | 1.43% | $25.1M | trimmed -11.2% | 2025 Q4 |
| 325 Capital LLC (focused) | 2.01M | 1.35% | $23.8M | unchanged | 2025 Q3 |
| Kennedy Capital Management LLC | 1.75M | 1.18% | $20.8M | added +22.1% | 2021 Q1 |
| Jane Street | 1.67M | 1.13% | $19.8M | added +338.7% | 2020 Q3 |
| No Street GP LP (focused) | 1.63M | 1.10% | $19.3M | added +10.4% | 2025 Q4 |
| Schonfeld Strategic Advisors | 1.61M | 1.08% | $19.1M | added +105.9% | 2025 Q2 |
| Goldman Sachs | 1.50M | 1.01% | $17.8M | trimmed -14.8% | 2020 Q3 |
| Balyasny Asset Management | 1.50M | 1.01% | $17.8M | added +71.8% | 2025 Q2 |
| Royce & Associates | 1.37M | 0.92% | $16.2M | added +17.1% | 2020 Q3 |
| Maestria Partners LLC (focused) | 1.36M | 0.92% | $16.2M | unchanged | 2024 Q4 |
| Blue Grotto Capital, LLC (focused) | 1.33M | 0.90% | $15.8M | trimmed -18.4% | 2025 Q2 |
| Northern Trust | 1.32M | 0.89% | $15.7M | added +4% | 2020 Q3 |
| Victory Capital Management INC | 1.27M | 0.85% | $15.0M | added +738.3% | 2020 Q3 |
| Grizzlyrock Capital, LLC (focused) | 1.24M | 0.84% | $14.7M | added +116.6% | 2023 Q4 |
| Millennium Management | 1.23M | 0.83% | $14.7M | added +5099% | 2020 Q3 |
| Charles Schwab Investment Management | 1.18M | 0.80% | $14.0M | trimmed -0.6% | 2020 Q3 |
| BNY Mellon | 1.14M | 0.77% | $13.5M | trimmed -3.8% | 2020 Q3 |
| Bank OF America CORP /DE/ | 1.13M | 0.76% | $13.4M | added +72.6% | 2020 Q3 |
| Citadel Advisors | 1.05M | 0.71% | $12.5M | added +93.4% | 2020 Q3 |
| Meros Investment Management, LP | 992.4k | 0.67% | $11.8M | added +20.2% | 2021 Q4 |
| Morgan Stanley | 926.8k | 0.63% | $11.0M | trimmed -50.2% | 2020 Q3 |
| Kopion Asset Management, LLC (focused) | 855.9k | 0.58% | $10.2M | added +39.3% | 2020 Q3 |
| UBS | 773.4k | 0.52% | $9.2M | added +5.6% | 2020 Q3 |
| Man Group | 664.0k | 0.45% | $7.9M | added +113.1% | 2025 Q4 |
| Qube Research & Technologies LTD | 661.1k | 0.45% | $7.8M | added +225.7% | 2023 Q1 |
| Oberweis Asset Management INC/ | 647.6k | 0.44% | $7.7M | added +1.9% | 2024 Q2 |
| Picton Mahoney Asset Management | 643.1k | 0.43% | $7.6M | added +65.7% | 2025 Q2 |
| Silvercrest Asset Management Group LLC | 616.1k | 0.42% | $7.3M | trimmed -10.1% | 2020 Q4 |
| Park West Asset Management LLC (focused) | 598.4k | 0.40% | $7.1M | opened | 2026 Q1 |
| Nomura Asset Management CO LTD | 593.9k | 0.40% | $7.0M | trimmed -4.6% | 2024 Q3 |
| CenterBook Partners LP | 564.2k | 0.38% | $6.7M | added +227% | 2024 Q4 |
| King Luther Capital Management CORP | 531.1k | 0.36% | $6.3M | added +3% | 2020 Q3 |
| Capital Group (American Funds) | 456.7k | 0.31% | $5.4M | opened | 2026 Q1 |
| QVT Financial LP | 453.9k | 0.31% | $5.4M | added +640.6% | 2025 Q4 |
| First Eagle Investment Management | 450.3k | 0.30% | $5.3M | added +51.9% | 2024 Q4 |
| Principal Financial Group INC | 445.9k | 0.30% | $5.3M | added +88% | 2020 Q3 |
Largest 50 of 286 shown; the full ranked, searchable register is at boothcheck.com/holders/MGNI. Related filers are grouped using the filings' own included-manager declarations. Historically, several managers opening new positions in the same quarter said almost nothing about the quarter that followed (59,118 cases since 2013). A filed record, not a forecast. Nothing here is investment advice.