Who owns MBX (MBX)
Which tracked institutional funds hold MBX, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See MBX company fundamentals →
Ownership as of the 2026-Q1 13F filings. 13F is disclosed up to 45 days after quarter-end, so the most recent quarter fills in over the following weeks.
How the tape is positioned
34 tracked funds added or opened MBX while 49 trimmed or exited it between 2025-Q4 and 2026-Q1 — the tape is split. When large holders disagree on a name, the funds moving first are sometimes ahead of the story.
A prompt to read the filings, not a verdict. 13F is a quarter-end snapshot disclosed up to 45 days late; a fund adds or exits for mandate, benchmark, and timing reasons that have nothing to do with a view on the stock. This is a starting question, not a signal to trade.
Conviction spread
MBX’s largest tracked holder by dollar value, Frazier Life Sciences Management, L.P., sizes it at 5.1% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 5.1pp conviction gap — its largest holder concentrates the name more heavily than the typical one.
Book-share is each fund’s reported value in MBX divided by its whole reported 13F book, so it is comparable across funds of different sizes and is unaffected by stock splits. A higher share means a fund has committed more of its book to the name — a starting question about conviction, not a verdict or a signal to trade.
Institutional & insider positioning
Between 2025-Q4 and 2026-Q1, across 157 tracked filers holding MBX, 83 increased or opened the position and 69 reduced or closed it; over the same quarter, open-market insider Form 4s were net purchases.
This fuses two public signals for the same quarter — how tracked institutions changed their positions and whether insiders bought or sold in the open market. It describes what was filed; it is a starting question, not a verdict or a signal to trade.
New buyers & exits
Funds opening or closing a position in MBX between the 2025-Q4 and 2026-Q1 13F filings, and the largest changes among funds holding it in both. New buyers and exits are counted on fund presence (split-invariant); adds and trims are measured on reported value.
New buyers 16
- Polar Capital Holdings Plc$48M
- VANGUARD CAPITAL MANAGEMENT LLC$44M
- Caligan Partners LP$25M
- Candriam S.C.A.$9M
- VANGUARD PORTFOLIO MANAGEMENT LLC$9M
- BOOTHBAY FUND MANAGEMENT, LLC$6M
Full exits 12
- VANGUARD GROUP INC$52M
- Point72 Asset Management, L.P.$21M
- Trails Edge Capital Partners, LP$10M
- Balyasny Asset Management L.P.$4M
- JANE STREET GROUP, LLC$3M
- Hudson Bay Capital Management LP$1M
Largest adds
- FMR LLC$84M
- Aaron Wealth Advisors LLC$33M
- STEMPOINT CAPITAL LP$12M
- BRAIDWELL LP$12M
- PRICE T ROWE ASSOCIATES INC /MD/$4M
- JPMORGAN CHASE & CO$3M
Largest trims
- EcoR1 Capital, LLC$44M
- Deep Track Capital, LP$20M
- ORBIMED ADVISORS LLC$16M
- Driehaus Capital Management LLC$14M
- WELLINGTON MANAGEMENT GROUP LLP$13M
- D. E. Shaw & Co., Inc.$13M
Institutional holders
One row per tracked fund, largest reported value first. “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding. Rows marked stale are from an earlier filing than the security’s latest quarter — that fund is absent from the newest snapshot (position exited, or reported under a different name).
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| Frazier Life Sciences Management, L.P. | 6,652,013 | $199M | 11.6% | 2026-Q1 |
| ORBIMED ADVISORS LLC trimmed | 3,637,887 | $109M | 6.4% | 2026-Q1 |
| NEA Management Company, LLC | 3,614,486 | $108M | 6.3% | 2026-Q1 |
| WELLINGTON MANAGEMENT GROUP LLP trimmed | 3,091,582 | $92M | 5.4% | 2026-Q1 |
| BlackRock, Inc. added | 2,941,406 | $88M | 5.2% | 2026-Q1 |
| FMR LLC added | 2,844,326 | $85M | 5.0% | 2026-Q1 |
| Deep Track Capital, LP trimmed | 2,757,569 | $82M | 4.8% | 2026-Q1 |
| NVP ASSOCIATES, LLC | 2,136,335 | $64M | 3.7% | 2026-Q1 |
| Polar Capital Holdings Plc new | 1,622,186 | $48M | 2.8% | 2026-Q1 |
| BRAIDWELL LP added | 1,492,467 | $45M | 2.6% | 2026-Q1 |
| VANGUARD CAPITAL MANAGEMENT LLC new | 1,477,592 | $44M | 2.6% | 2026-Q1 |
| Aaron Wealth Advisors LLC added | 1,168,176 | $35M | 2.0% | 2026-Q1 |
| Cormorant Asset Management, LP | 1,120,000 | $33M | 2.0% | 2026-Q1 |
| PRICE T ROWE ASSOCIATES INC /MD/ added | 1,029,007 | $31M | 1.8% | 2026-Q1 |
| Driehaus Capital Management LLC trimmed | 1,018,212 | $30M | 1.8% | 2026-Q1 |
| Kynam Capital Management, LP | 934,799 | $28M | 1.6% | 2026-Q1 |
| CITADEL ADVISORS LLC added | 932,833 | $28M | 1.6% | 2026-Q1 |
| Woodline Partners LP trimmed | 900,063 | $27M | 1.6% | 2026-Q1 |
| EVENTIDE ASSET MANAGEMENT, LLC | 890,000 | $27M | 1.6% | 2026-Q1 |
| Caligan Partners LP new | 848,590 | $25M | 1.5% | 2026-Q1 |
| Parkman Healthcare Partners LLC trimmed | 800,037 | $24M | 1.4% | 2026-Q1 |
| STATE STREET CORP added | 787,208 | $23M | 1.4% | 2026-Q1 |
| EcoR1 Capital, LLC trimmed | 777,000 | $23M | 1.4% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 670,385 | $20M | 1.2% | 2026-Q1 |
| TCG Crossover Management, LLC | 650,000 | $19M | 1.1% | 2026-Q1 |
| MILLENNIUM MANAGEMENT LLC added | 564,415 | $17M | 1.0% | 2026-Q1 |
| STEMPOINT CAPITAL LP added | 499,469 | $15M | 0.9% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC added | 457,945 | $14M | 0.8% | 2026-Q1 |
| UBS Group AG added | 346,914 | $10M | 0.6% | 2026-Q1 |
| Candriam S.C.A. new | 294,374 | $9M | 0.5% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 293,295 | $9M | 0.5% | 2026-Q1 |
| D. E. Shaw & Co., Inc. trimmed | 288,889 | $9M | 0.5% | 2026-Q1 |
| Rock Springs Capital Management LP added | 287,967 | $9M | 0.5% | 2026-Q1 |
| Opaleye Management Inc. | 260,000 | $8M | 0.5% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 214,908 | $6M | 0.4% | 2026-Q1 |
| Elmind Capital, LP | 211,000 | $6M | 0.4% | 2026-Q1 |
| NORTHERN TRUST CORP added | 210,575 | $6M | 0.4% | 2026-Q1 |
| BOOTHBAY FUND MANAGEMENT, LLC added | 208,049 | $6M | 0.4% | 2026-Q1 |
| Soleus Capital Management, L.P. trimmed | 178,897 | $5M | 0.3% | 2026-Q1 |
| DAFNA Capital Management LLC added | 175,465 | $5M | 0.3% | 2026-Q1 |
| VANGUARD FIDUCIARY TRUST CO new | 170,154 | $5M | 0.3% | 2026-Q1 |
| Goelzer Investment Management, Inc. trimmed | 164,172 | $5M | 0.3% | 2026-Q1 |
| Affinity Asset Advisors, LLC trimmed | 150,000 | $4M | 0.3% | 2026-Q1 |
| Tetragon Partners GP Ltd added | 145,480 | $4M | 0.3% | 2026-Q1 |
| JPMORGAN CHASE & CO added | 147,057 | $4M | 0.2% | 2026-Q1 |
| Schonfeld Strategic Advisors LLC trimmed | 123,814 | $4M | 0.2% | 2026-Q1 |
| KVP Capital Advisors, LP | 121,524 | $4M | 0.2% | 2026-Q1 |
| TD Asset Management Inc added | 115,998 | $3M | 0.2% | 2026-Q1 |
| TWO SIGMA INVESTMENTS, LP trimmed | 115,075 | $3M | 0.2% | 2026-Q1 |
| Burkehill Global Management, LP | 100,000 | $3M | 0.2% | 2026-Q1 |
| Squarepoint Ops LLC added | 97,215 | $3M | 0.2% | 2026-Q1 |
| MANUFACTURERS LIFE INSURANCE COMPANY, THE added | 90,634 | $3M | 0.2% | 2026-Q1 |
| Nuveen, LLC added | 81,792 | $2M | 0.1% | 2026-Q1 |
| Bank of New York Mellon Corp added | 80,222 | $2M | 0.1% | 2026-Q1 |
| PFM Health Sciences, LP trimmed | 71,894 | $2M | 0.1% | 2026-Q1 |
| VICTORY CAPITAL MANAGEMENT INC new | 71,028 | $2M | 0.1% | 2026-Q1 |
| MARSHALL WACE, LLP trimmed | 62,703 | $2M | 0.1% | 2026-Q1 |
| XTX Topco Ltd added | 53,210 | $2M | 0.1% | 2026-Q1 |
| SCHRODER INVESTMENT MANAGEMENT GROUP trimmed | 57,322 | $2M | 0.1% | 2026-Q1 |
| DIMENSIONAL FUND ADVISORS LP new | 46,753 | $1M | 0.1% | 2026-Q1 |
| Swiss National Bank new | 44,400 | $1M | 0.1% | 2026-Q1 |
| PLATINUM INVESTMENT MANAGEMENT LTD | 43,597 | $1M | 0.1% | 2026-Q1 |
| ALPS ADVISORS INC trimmed | 36,550 | $1M | 0.1% | 2026-Q1 |
| ALGERT GLOBAL LLC new | 36,020 | $1M | 0.1% | 2026-Q1 |
| Creative Planning added | 35,970 | $1M | 0.1% | 2026-Q1 |
| EXCHANGE TRADED CONCEPTS, LLC new | 34,264 | $1M | 0.1% | 2026-Q1 |
| RHUMBLINE ADVISERS added | 33,871 | $1M | 0.1% | 2026-Q1 |
| ALLIANCEBERNSTEIN L.P. added | 30,500 | $962K | 0.1% | 2026-Q1 |
| MORGAN STANLEY trimmed | 31,562 | $942K | 0.1% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ trimmed | 28,750 | $858K | 0.1% | 2026-Q1 |
| ExodusPoint Capital Management, LP trimmed | 28,087 | $838K | 0.0% | 2026-Q1 |
| Invesco Ltd. added | 27,525 | $822K | 0.0% | 2026-Q1 |
| AQR CAPITAL MANAGEMENT LLC trimmed | 26,784 | $800K | 0.0% | 2026-Q1 |
| DEUTSCHE BANK AG\ added | 22,950 | $685K | 0.0% | 2026-Q1 |
| CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM added | 22,765 | $680K | 0.0% | 2026-Q1 |
| Swiss Life Asset Management Ltd new | 12,130 | $657K | 0.0% | 2026-Q1 |
| Cerity Partners LLC trimmed | 21,163 | $632K | 0.0% | 2026-Q1 |
| VANGUARD GROUP INC trimmed | 1,636,879 | $52M | 3.0% | 2025-Q4 stale |
| FRANKLIN RESOURCES INC added | 1,307,288 | $23M | 1.3% | 2025-Q3 stale |
| Point72 Asset Management, L.P. added | 680,609 | $21M | 1.3% | 2025-Q4 stale |
| MPM BIOIMPACT LLC added | 1,294,416 | $15M | 0.9% | 2025-Q2 stale |
| Trails Edge Capital Partners, LP new | 315,158 | $10M | 0.6% | 2025-Q4 stale |
| BAKER BROS. ADVISORS LP new | 277,777 | $5M | 0.3% | 2025-Q3 stale |
| RA CAPITAL MANAGEMENT, L.P. trimmed | 377,841 | $4M | 0.3% | 2025-Q2 stale |
| Longaeva Partners L.P. new | 224,433 | $4M | 0.2% | 2025-Q3 stale |
| Balyasny Asset Management L.P. added | 119,726 | $4M | 0.2% | 2025-Q4 stale |
| SECTORAL ASSET MANAGEMENT INC added | 194,898 | $3M | 0.2% | 2025-Q3 stale |
| Sio Capital Management, LLC new | 241,000 | $3M | 0.2% | 2025-Q2 stale |
| JANE STREET GROUP, LLC added | 86,581 | $3M | 0.2% | 2025-Q4 stale |
| Hudson Bay Capital Management LP | 85,000 | $1M | 0.1% | 2025-Q4 stale |
| Murchinson Ltd. new | 80,000 | $1M | 0.1% | 2025-Q3 stale |
| RENAISSANCE TECHNOLOGIES LLC new | 32,644 | $1M | 0.1% | 2025-Q4 stale |
| Exome Asset Management LLC trimmed | 52,402 | $917K | 0.1% | 2025-Q3 stale |
| Ikarian Capital, LLC new | 48,071 | $841K | 0.0% | 2025-Q3 stale |
| Brevan Howard Capital Management LP new | 25,663 | $809K | 0.0% | 2025-Q4 stale |
| Trexquant Investment LP new | 24,268 | $765K | 0.0% | 2025-Q4 stale |
| FOX RUN MANAGEMENT, L.L.C. new | 23,820 | $751K | 0.0% | 2025-Q4 stale |
| READYSTATE ASSET MANAGEMENT LP new | 38,500 | $674K | 0.0% | 2025-Q3 stale |
| Ghisallo Capital Management LLC added | 38,250 | $669K | 0.0% | 2025-Q3 stale |
| NORGES BANK | 25,000 | $650K | 0.0% | 2025-Q3 stale |
Ownership over time
Tracked institutional holder count and total shares held by filing quarter (independent scales). The curated-era tail and any mid-ingest latest quarter are handled honestly — a partial quarter is not drawn as a collapse.
Reading this table
Funds hold the same stock for different reasons — an index fund “holds” almost everything, an active manager sizes a name to a mandate and a benchmark, and each fund entered at its own price and time. Because 13F is filed up to 45 days after quarter-end, every row is a backward-looking snapshot; a manager may have traded since. Share-class siblings (a company’s A and C shares) are rolled up to one line so a dual-class name is never double-counted. Compare like-for-like. A large holder is not an endorsement, and a fund exiting is not a warning — this is a starting question, not a verdict.
About 13F filings
A Form 13F is a quarterly disclosure that institutional investment managers with over $100 million in US-listed equities must file with the SEC. In plain English: it is a snapshot of the long stock positions a fund held at the end of a quarter. It covers long US-listed equities only — not short positions, options, cash, or private holdings — and the funds shown are the large sample we track, not the complete 13F universe.