Mar 31, 2026 filings. Quarterly 13F reports arrive up to 45 days after quarter end; this register is filed through May 29, 2026.
648 institutional managers reported holding INSM for the quarter ended Mar 31, 2026. Together they hold about 89% of shares outstanding; the top 10 hold 48%. 89 opened new positions; 104 closed out. Complete ranked register from SEC 13F filings.
| manager | shares | % out | value (Mar 31, 2026 close) | change | held since |
|---|---|---|---|---|---|
| Vanguard Group | 21.95M | 10.19% | $3.59B | added +4.1% | ≤2013 |
| Darwin Global Management, LTD. (focused) | 16.81M | 7.80% | $2.75B | trimmed -19.7% | 2024 Q2 |
| BlackRock | 16.68M | 7.74% | $2.73B | added +10.7% | ≤2013 |
| FMR (Fidelity) | 13.16M | 6.11% | $2.15B | added +32.6% | ≤2013 |
| Baker Bros. Advisors LP | 7.42M | 3.44% | $1.21B | added +12.6% | ≤2013 |
| Artisan Partners | 6.53M | 3.03% | $1.07B | added +34.8% | 2024 Q2 |
| D. E. Shaw | 5.63M | 2.61% | $919.9M | added +29.3% | ≤2013 |
| Capital International Investors | 5.60M | 2.60% | $914.9M | added +8.6% | 2024 Q1 |
| State Street | 5.55M | 2.58% | $907.8M | added +6.7% | ≤2013 |
| RTW Investments, LP | 4.84M | 2.25% | $791.9M | unchanged | 2023 Q2 |
| Geode Capital | 4.45M | 2.06% | $727.7M | added +3.5% | ≤2013 |
| T. Rowe Price | 3.09M | 1.44% | $505.7M | trimmed -23.4% | 2014 Q1 |
| Ameriprise Financial INC | 3.06M | 1.42% | $500.0M | added +55.3% | ≤2013 |
| UBS | 2.95M | 1.37% | $482.8M | added +5% | ≤2013 |
| Franklin Resources | 2.62M | 1.22% | $428.0M | trimmed -5% | 2019 Q2 |
| Citadel Advisors | 2.18M | 1.01% | $356.9M | added +88.6% | 2018 Q2 |
| Invesco | 1.99M | 0.92% | $325.2M | trimmed -27.1% | 2016 Q4 |
| Orbis Allan Gray LTD | 1.87M | 0.87% | $306.2M | trimmed -55.2% | 2025 Q2 |
| Bank OF America CORP /DE/ | 1.50M | 0.70% | $245.7M | trimmed -12.9% | ≤2013 |
| Integral Health Asset Management, LLC | 1.50M | 0.70% | $245.3M | added +20% | 2023 Q4 |
| Westfield Capital Management CO LP | 1.47M | 0.68% | $240.1M | added +239.5% | 2024 Q3 |
| SEI Investments CO | 1.40M | 0.65% | $228.2M | added +56.8% | 2017 Q2 |
| Capital Group (American Funds) | 1.36M | 0.63% | $222.8M | opened | 2026 Q1 |
| Morgan Stanley | 1.33M | 0.62% | $217.7M | trimmed -18.4% | ≤2013 |
| Northern Trust | 1.29M | 0.60% | $211.6M | added +4.5% | ≤2013 |
| Castle Hook Partners LP (focused) | 1.27M | 0.59% | $207.6M | added +1.3% | 2025 Q2 |
| BNY Mellon | 1.26M | 0.59% | $206.5M | trimmed -9.2% | ≤2013 |
| Paradigm Biocapital Advisors LP (focused) | 1.25M | 0.58% | $205.1M | opened | 2026 Q1 |
| Nomura Asset Management International INC. | 1.16M | 0.54% | $190.1M | trimmed -4.2% | 2025 Q4 |
| Millennium Management | 1.16M | 0.54% | $189.3M | trimmed -11.7% | 2019 Q4 |
| Duquesne Family Office | 1.15M | 0.54% | $188.7M | trimmed -22.1% | 2024 Q2 |
| Pictet Asset Management Holding SA | 1.10M | 0.51% | $180.2M | added +14.9% | 2020 Q3 |
| BNP Paribas Financial Markets | 1.07M | 0.50% | $175.4M | trimmed -13.8% | 2014 Q1 |
| Charles Schwab Investment Management | 1.07M | 0.50% | $174.9M | added +4.1% | ≤2013 |
| Fiera Capital CORP | 1.02M | 0.47% | $167.1M | added +2.9% | 2024 Q2 |
| NWI Management LP (focused) | 1.01M | 0.47% | $165.8M | added +2.6% | 2024 Q3 |
| Goldman Sachs | 942.6k | 0.44% | $154.1M | trimmed -24.3% | 2013 Q3 |
| American Century Companies INC | 925.8k | 0.43% | $151.4M | added +400.2% | 2018 Q2 |
| Principal Financial Group INC | 921.7k | 0.43% | $150.7M | added +18.7% | ≤2013 |
| William Blair Investment Management, LLC | 902.7k | 0.42% | $147.6M | trimmed -26.1% | 2020 Q1 |
| Adage Capital Partners GP, L.l.c. | 900.0k | 0.42% | $147.2M | added +200% | 2023 Q3 |
| FIL LTD | 828.9k | 0.39% | $135.5M | trimmed -1.1% | 2022 Q3 |
| Amundi | 805.0k | 0.37% | $131.6M | trimmed -12.2% | 2024 Q4 |
| Legal & General Group PLC | 787.1k | 0.36% | $128.7M | added +45.7% | 2014 Q3 |
| Raymond James Financial INC | 775.1k | 0.36% | $126.8M | trimmed -0.5% | 2018 Q3 |
| AllianceBernstein | 688.7k | 0.32% | $112.6M | added +7.2% | ≤2013 |
| Hood River Capital Management LLC | 688.6k | 0.32% | $112.6M | added +8% | 2023 Q4 |
| AQR Capital | 675.5k | 0.31% | $110.5M | added +44.3% | 2015 Q2 |
| Summit Partners Public Asset Management, LLC | 653.4k | 0.30% | $106.9M | trimmed -28.1% | 2023 Q4 |
| Clearbridge Investments, LLC | 643.4k | 0.30% | $105.2M | trimmed -21.4% | 2024 Q1 |
Largest 50 of 648 shown; the full ranked, searchable register is at boothcheck.com/holders/INSM. 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.