Who owns MBX Biosciences, Inc. Common Stock (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-Q2 13F filings (latest filed 2026-09-22). 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
The tracked-fund tape on MBX is one-sided between 2026-Q1 and 2026-Q2: 89 added or opened and 20 trimmed or exited — on balance accumulating.
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 8.0% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 8.0pp 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 2026-Q1 and 2026-Q2, across 169 tracked filers holding MBX, 99 increased or opened the position and 76 reduced or closed it; over the same quarter, open-market insider Form 4s were net sales.
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 2026-Q1 and 2026-Q2 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 12
- Paradigm Biocapital Advisors LP$138M
- FRANKLIN RESOURCES INC$14M
- PRUDENTIAL FINANCIAL INC$5M
- MOORE CAPITAL MANAGEMENT, LP$4M
- Rhenman & Partners Asset Management AB$3M
- Ensign Peak Advisors, Inc$2M
Full exits 9
- CITADEL ADVISORS LLC$26M
- STEMPOINT CAPITAL LP$15M
- Squarepoint Ops LLC$3M
- VICTORY CAPITAL MANAGEMENT INC$2M
- SCHRODER INVESTMENT MANAGEMENT GROUP$2M
- ExodusPoint Capital Management, LP$838K
Largest adds
- FMR LLC$209M
- WELLINGTON MANAGEMENT GROUP LLP$182M
- Frazier Life Sciences Management, L.P.$169M
- BlackRock, Inc.$96M
- NEA Management Company, LLC$92M
- ORBIMED ADVISORS LLC$81M
Largest trims
- Caligan Partners LP$14M
- BRAIDWELL LP$5M
- Goelzer Investment Management, Inc.$5M
- DAFNA Capital Management LLC$5M
- MILLENNIUM MANAGEMENT LLC$4M
- Cormorant Asset Management, LP$3M
Institutional holders
One row per tracked fund, most shares held first (every row is from one quarter; reported value breaks ties). “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding.
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| Frazier Life Sciences Management, L.P. | 6,652,013 | $367M | 12.0% | 2026-Q2 |
| FMR LLC added | 5,322,885 | $294M | 9.6% | 2026-Q2 |
| WELLINGTON MANAGEMENT GROUP LLP added | 4,977,523 | $275M | 9.0% | 2026-Q2 |
| NEA Management Company, LLC | 3,614,486 | $200M | 6.5% | 2026-Q2 |
| ORBIMED ADVISORS LLC trimmed | 3,428,736 | $189M | 6.2% | 2026-Q2 |
| BlackRock, Inc. added | 3,323,672 | $183M | 6.0% | 2026-Q2 |
| Paradigm Biocapital Advisors LP new | 2,508,015 | $138M | 4.5% | 2026-Q2 |
| NVP ASSOCIATES, LLC | 2,136,335 | $118M | 3.9% | 2026-Q2 |
| Deep Track Capital, LP trimmed | 1,732,569 | $96M | 3.1% | 2026-Q2 |
| Polar Capital Holdings Plc trimmed | 1,608,514 | $89M | 2.9% | 2026-Q2 |
| VANGUARD CAPITAL MANAGEMENT LLC trimmed | 1,477,388 | $82M | 2.7% | 2026-Q2 |
| Aaron Wealth Advisors LLC trimmed | 1,167,799 | $64M | 2.1% | 2026-Q2 |
| Driehaus Capital Management LLC added | 1,056,579 | $58M | 1.9% | 2026-Q2 |
| Kynam Capital Management, LP | 934,799 | $52M | 1.7% | 2026-Q2 |
| Woodline Partners LP added | 900,092 | $50M | 1.6% | 2026-Q2 |
| EVENTIDE ASSET MANAGEMENT, LLC trimmed | 873,492 | $48M | 1.6% | 2026-Q2 |
| STATE STREET CORP added | 864,466 | $48M | 1.6% | 2026-Q2 |
| PRICE T ROWE ASSOCIATES INC /MD/ trimmed | 814,807 | $45M | 1.5% | 2026-Q2 |
| Parkman Healthcare Partners LLC added | 800,173 | $44M | 1.4% | 2026-Q2 |
| GEODE CAPITAL MANAGEMENT, LLC added | 773,072 | $43M | 1.4% | 2026-Q2 |
| BRAIDWELL LP trimmed | 710,880 | $39M | 1.3% | 2026-Q2 |
| TCG Crossover Management, LLC | 650,000 | $36M | 1.2% | 2026-Q2 |
| Cormorant Asset Management, LP trimmed | 550,000 | $30M | 1.0% | 2026-Q2 |
| Soleus Capital Management, L.P. added | 515,279 | $28M | 0.9% | 2026-Q2 |
| GOLDMAN SACHS GROUP INC added | 459,005 | $25M | 0.8% | 2026-Q2 |
| MARSHALL WACE, LLP added | 401,885 | $22M | 0.7% | 2026-Q2 |
| EcoR1 Capital, LLC trimmed | 388,500 | $21M | 0.7% | 2026-Q2 |
| VANGUARD PORTFOLIO MANAGEMENT LLC added | 346,717 | $19M | 0.6% | 2026-Q2 |
| BANK OF AMERICA CORP /DE/ added | 298,927 | $17M | 0.5% | 2026-Q2 |
| Rock Springs Capital Management LP added | 298,218 | $16M | 0.5% | 2026-Q2 |
| Candriam S.C.A. trimmed | 289,893 | $16M | 0.5% | 2026-Q2 |
| UBS Group AG trimmed | 272,747 | $15M | 0.5% | 2026-Q2 |
| Opaleye Management Inc. | 260,000 | $14M | 0.5% | 2026-Q2 |
| FRANKLIN RESOURCES INC trimmed | 252,665 | $14M | 0.5% | 2026-Q2 |
| Schonfeld Strategic Advisors LLC added | 248,670 | $14M | 0.5% | 2026-Q2 |
| MORGAN STANLEY added | 248,558 | $14M | 0.4% | 2026-Q2 |
| NORTHERN TRUST CORP added | 246,678 | $14M | 0.4% | 2026-Q2 |
| DIMENSIONAL FUND ADVISORS LP added | 233,700 | $13M | 0.4% | 2026-Q2 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC added | 233,095 | $13M | 0.4% | 2026-Q2 |
| MILLENNIUM MANAGEMENT LLC trimmed | 226,151 | $12M | 0.4% | 2026-Q2 |
| Tetragon Partners GP Ltd added | 203,543 | $11M | 0.4% | 2026-Q2 |
| VANGUARD FIDUCIARY TRUST CO added | 201,429 | $11M | 0.4% | 2026-Q2 |
| Caligan Partners LP trimmed | 200,000 | $11M | 0.4% | 2026-Q2 |
| D. E. Shaw & Co., Inc. trimmed | 182,767 | $10M | 0.3% | 2026-Q2 |
| JPMORGAN CHASE & CO trimmed | 139,611 | $8M | 0.2% | 2026-Q2 |
| KVP Capital Advisors, LP | 121,524 | $7M | 0.2% | 2026-Q2 |
| TWO SIGMA INVESTMENTS, LP trimmed | 113,475 | $6M | 0.2% | 2026-Q2 |
| Burkehill Global Management, LP | 100,000 | $6M | 0.2% | 2026-Q2 |
| Nuveen, LLC added | 98,733 | $5M | 0.2% | 2026-Q2 |
| TD Asset Management Inc trimmed | 95,598 | $5M | 0.2% | 2026-Q2 |
| Elmind Capital, LP trimmed | 91,000 | $5M | 0.2% | 2026-Q2 |
| Bank of New York Mellon Corp added | 88,927 | $5M | 0.2% | 2026-Q2 |
| PRUDENTIAL FINANCIAL INC new | 88,045 | $5M | 0.2% | 2026-Q2 |
| BARCLAYS PLC added | 87,854 | $5M | 0.2% | 2026-Q2 |
| Affinity Asset Advisors, LLC trimmed | 75,000 | $4M | 0.1% | 2026-Q2 |
| PFM Health Sciences, LP trimmed | 70,971 | $4M | 0.1% | 2026-Q2 |
| BOOTHBAY FUND MANAGEMENT, LLC trimmed | 70,353 | $4M | 0.1% | 2026-Q2 |
| MANUFACTURERS LIFE INSURANCE COMPANY, THE trimmed | 66,112 | $4M | 0.1% | 2026-Q2 |
| MOORE CAPITAL MANAGEMENT, LP new | 64,893 | $4M | 0.1% | 2026-Q2 |
| Rhenman & Partners Asset Management AB new | 62,000 | $3M | 0.1% | 2026-Q2 |
| Invesco Ltd. added | 50,678 | $3M | 0.1% | 2026-Q2 |
| ALPS ADVISORS INC added | 48,012 | $3M | 0.1% | 2026-Q2 |
| PLATINUM INVESTMENT MANAGEMENT LTD | 43,597 | $2M | 0.1% | 2026-Q2 |
| Swiss National Bank trimmed | 42,900 | $2M | 0.1% | 2026-Q2 |
| Ensign Peak Advisors, Inc new | 42,156 | $2M | 0.1% | 2026-Q2 |
| ALGERT GLOBAL LLC added | 42,070 | $2M | 0.1% | 2026-Q2 |
| Creative Planning added | 39,524 | $2M | 0.1% | 2026-Q2 |
| RHUMBLINE ADVISERS added | 37,196 | $2M | 0.1% | 2026-Q2 |
| DEUTSCHE BANK AG\ added | 31,693 | $2M | 0.1% | 2026-Q2 |
| ALLIANCEBERNSTEIN L.P. added | 31,000 | $925K | 0.0% | 2026-Q2 |
| WELLS FARGO & COMPANY/MN added | 28,313 | $2M | 0.1% | 2026-Q2 |
| EXCHANGE TRADED CONCEPTS, LLC trimmed | 27,421 | $2M | 0.0% | 2026-Q2 |
| SUSQUEHANNA INTERNATIONAL GROUP, LLP added | 26,684 | $1M | 0.0% | 2026-Q2 |
| VOYA INVESTMENT MANAGEMENT LLC new | 26,132 | $1M | 0.0% | 2026-Q2 |
| Universal- Beteiligungs- und Servicegesellschaft mbH trimmed | 25,800 | $1M | 0.0% | 2026-Q2 |
| CITIGROUP INC added | 25,122 | $1M | 0.0% | 2026-Q2 |
| CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM added | 23,376 | $1M | 0.0% | 2026-Q2 |
| AMERICAN CENTURY COMPANIES INC added | 22,680 | $1M | 0.0% | 2026-Q2 |
| AQR CAPITAL MANAGEMENT LLC trimmed | 22,591 | $1M | 0.0% | 2026-Q2 |
| Legal & General Group Plc added | 21,583 | $1M | 0.0% | 2026-Q2 |
| UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC added | 21,344 | $1M | 0.0% | 2026-Q2 |
| Cerity Partners LLC trimmed | 20,997 | $1M | 0.0% | 2026-Q2 |
| Vanguard Global Advisers, LLC added | 18,969 | $1M | 0.0% | 2026-Q2 |
| MetLife Investment Management, LLC added | 18,250 | $1M | 0.0% | 2026-Q2 |
| Russell Investments Group, Ltd. added | 18,162 | $1M | 0.0% | 2026-Q2 |
| Koa Wealth Management, LLC trimmed | 17,113 | $945K | 0.0% | 2026-Q2 |
| STATE OF WISCONSIN INVESTMENT BOARD trimmed | 15,971 | $882K | 0.0% | 2026-Q2 |
| VANGUARD ASSET MANAGEMENT, Ltd | 14,752 | $814K | 0.0% | 2026-Q2 |
| Sound Capital Solutions LLC new | 14,458 | $798K | 0.0% | 2026-Q2 |
| OPTIMIZE FINANCIAL INC. trimmed | 14,458 | $798K | 0.0% | 2026-Q2 |
| MIRAE ASSET GLOBAL ETFS HOLDINGS Ltd. added | 14,292 | $789K | 0.0% | 2026-Q2 |
| DAFNA Capital Management LLC trimmed | 11,809 | $652K | 0.0% | 2026-Q2 |
| HighVista Strategies LLC added | 11,634 | $642K | 0.0% | 2026-Q2 |
| NEW YORK STATE COMMON RETIREMENT FUND added | 11,000 | $607K | 0.0% | 2026-Q2 |
| Jupiter Topco LLC new | 10,300 | $568K | 0.0% | 2026-Q2 |
| FRED ALGER MANAGEMENT, LLC new | 9,877 | $545K | 0.0% | 2026-Q2 |
| BNP PARIBAS FINANCIAL MARKETS trimmed | 9,860 | $544K | 0.0% | 2026-Q2 |
| STATE BOARD OF ADMINISTRATION OF FLORIDA RETIREMENT SYSTEM new | 9,777 | $540K | 0.0% | 2026-Q2 |
| Virtus Investment Advisers, LLC added | 9,215 | $509K | 0.0% | 2026-Q2 |
| China Universal Asset Management Co., Ltd. added | 9,175 | $506K | 0.0% | 2026-Q2 |
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.