Who owns Upstream Bio, Inc. (UPB)
Which tracked institutional funds hold UPB, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See UPB company fundamentals →
Ownership as of the 2026-Q1 13F filings (latest filed 2026-05-18). 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
23 tracked funds added or opened UPB while 61 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
UPB’s largest tracked holder by dollar value, FMR LLC, sizes it at 0.0% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 0.0pp gap the other way — the median holder sizes UPB more heavily than its largest holder by dollar value does.
Book-share is each fund’s reported value in UPB 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 142 tracked filers holding UPB, 93 increased or opened the position and 77 reduced or closed it; over the same quarter, open-market insider Form 4 buying and selling roughly offset.
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 UPB 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 14
- VANGUARD CAPITAL MANAGEMENT LLC$17M
- SEB Asset Management AB$8M
- VANGUARD PORTFOLIO MANAGEMENT LLC$7M
- HSBC HOLDINGS PLC$6M
- Qube Research & Technologies Ltd$6M
- SPHERA FUNDS MANAGEMENT LTD.$3M
Full exits 16
- VANGUARD GROUP INC$58M
- JANUS HENDERSON GROUP PLC$41M
- Omega Fund Management, LLC$36M
- VR ADVISER, LLC$32M
- Integral Health Asset Management, LLC$20M
- Vestal Point Capital, LP$20M
Largest adds
- FEDERATED HERMES, INC.$9M
- Y-Intercept (Hong Kong) Ltd$8M
- D. E. Shaw & Co., Inc.$7M
- MORGAN STANLEY$2M
- XTX Topco Ltd$1M
- Point72 Asset Management, L.P.$1M
Largest trims
- FMR LLC$139M
- ORBIMED ADVISORS LLC$103M
- NORGES BANK$72M
- Decheng Capital LLC$61M
- BlackRock, Inc.$60M
- UBS Group AG$47M
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 |
|---|---|---|---|---|
| FMR LLC trimmed | 7,210,151 | $65M | 9.5% | 2026-Q1 |
| ORBIMED ADVISORS LLC | 5,693,589 | $51M | 7.5% | 2026-Q1 |
| BlackRock, Inc. added | 3,370,689 | $30M | 4.5% | 2026-Q1 |
| Decheng Capital LLC trimmed | 2,724,868 | $25M | 3.6% | 2026-Q1 |
| ENAVATE SCIENCES GP, LLC | 2,459,703 | $22M | 3.2% | 2026-Q1 |
| VANGUARD CAPITAL MANAGEMENT LLC new | 1,873,574 | $17M | 2.5% | 2026-Q1 |
| Y-Intercept (Hong Kong) Ltd added | 1,000,631 | $9M | 1.3% | 2026-Q1 |
| FEDERATED HERMES, INC. added | 979,758 | $9M | 1.3% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 950,617 | $9M | 1.3% | 2026-Q1 |
| MILLENNIUM MANAGEMENT LLC added | 937,323 | $8M | 1.2% | 2026-Q1 |
| SEB Asset Management AB new | 878,473 | $8M | 1.2% | 2026-Q1 |
| Bain Capital Life Sciences Investors, LLC trimmed | 867,211 | $8M | 1.1% | 2026-Q1 |
| Woodline Partners LP added | 831,481 | $7M | 1.1% | 2026-Q1 |
| D. E. Shaw & Co., Inc. added | 820,480 | $7M | 1.1% | 2026-Q1 |
| Parkman Healthcare Partners LLC trimmed | 786,783 | $7M | 1.0% | 2026-Q1 |
| SAMSARA BIOCAPITAL, LLC | 736,047 | $7M | 1.0% | 2026-Q1 |
| Pictet Asset Management Holding SA trimmed | 733,431 | $7M | 1.0% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 727,711 | $7M | 1.0% | 2026-Q1 |
| STATE STREET CORP trimmed | 705,350 | $6M | 0.9% | 2026-Q1 |
| NORGES BANK trimmed | 969,916 | $6M | 0.9% | 2026-Q1 |
| HSBC HOLDINGS PLC new | 640,326 | $6M | 0.8% | 2026-Q1 |
| Qube Research & Technologies Ltd new | 619,321 | $6M | 0.8% | 2026-Q1 |
| MORGAN STANLEY added | 552,609 | $5M | 0.7% | 2026-Q1 |
| JPMORGAN CHASE & CO added | 463,001 | $4M | 0.6% | 2026-Q1 |
| Nantahala Capital Management, LLC trimmed | 400,000 | $4M | 0.5% | 2026-Q1 |
| Altshuler Shaham Ltd trimmed | 380,061 | $3M | 0.5% | 2026-Q1 |
| SPHERA FUNDS MANAGEMENT LTD. new | 358,000 | $3M | 0.5% | 2026-Q1 |
| Propel Bio Management, LLC new | 341,779 | $3M | 0.5% | 2026-Q1 |
| WELLINGTON MANAGEMENT GROUP LLP trimmed | 342,353 | $3M | 0.5% | 2026-Q1 |
| Jump Financial, LLC new | 319,400 | $3M | 0.4% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC trimmed | 316,587 | $3M | 0.4% | 2026-Q1 |
| Alyeska Investment Group, L.P. | 298,329 | $3M | 0.4% | 2026-Q1 |
| NORTHERN TRUST CORP added | 260,992 | $2M | 0.3% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 257,729 | $2M | 0.3% | 2026-Q1 |
| Prosight Management, LP new | 241,123 | $2M | 0.3% | 2026-Q1 |
| UBS Group AG trimmed | 231,254 | $2M | 0.3% | 2026-Q1 |
| VANGUARD FIDUCIARY TRUST CO new | 224,157 | $2M | 0.3% | 2026-Q1 |
| XTX Topco Ltd added | 209,277 | $2M | 0.3% | 2026-Q1 |
| ARROWSTREET CAPITAL, LIMITED PARTNERSHIP new | 185,087 | $2M | 0.2% | 2026-Q1 |
| TCG Crossover Management, LLC trimmed | 181,063 | $2M | 0.2% | 2026-Q1 |
| DEUTSCHE BANK AG\ added | 180,889 | $2M | 0.2% | 2026-Q1 |
| Point72 Asset Management, L.P. added | 178,168 | $2M | 0.2% | 2026-Q1 |
| Trexquant Investment LP added | 176,657 | $2M | 0.2% | 2026-Q1 |
| Schonfeld Strategic Advisors LLC added | 161,349 | $1M | 0.2% | 2026-Q1 |
| Boxer Capital Management, LLC | 150,000 | $1M | 0.2% | 2026-Q1 |
| BNP PARIBAS FINANCIAL MARKETS added | 126,000 | $1M | 0.2% | 2026-Q1 |
| ALLIANCEBERNSTEIN L.P. | 31,010 | $842K | 0.1% | 2026-Q1 |
| ExodusPoint Capital Management, LP added | 91,431 | $823K | 0.1% | 2026-Q1 |
| AMERICAN CENTURY COMPANIES INC trimmed | 87,624 | $789K | 0.1% | 2026-Q1 |
| Bank of New York Mellon Corp trimmed | 81,383 | $732K | 0.1% | 2026-Q1 |
| DIMENSIONAL FUND ADVISORS LP new | 80,002 | $719K | 0.1% | 2026-Q1 |
| Simplify Asset Management Inc. new | 77,793 | $700K | 0.1% | 2026-Q1 |
| Nuveen, LLC trimmed | 75,536 | $680K | 0.1% | 2026-Q1 |
| EntryPoint Capital, LLC new | 73,568 | $662K | 0.1% | 2026-Q1 |
| AQR CAPITAL MANAGEMENT LLC added | 70,556 | $635K | 0.1% | 2026-Q1 |
| MARSHALL WACE, LLP trimmed | 64,527 | $581K | 0.1% | 2026-Q1 |
| RENAISSANCE TECHNOLOGIES LLC added | 62,100 | $559K | 0.1% | 2026-Q1 |
| Quantinno Capital Management LP added | 49,389 | $445K | 0.1% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ trimmed | 48,460 | $436K | 0.1% | 2026-Q1 |
| Swiss National Bank added | 48,100 | $433K | 0.1% | 2026-Q1 |
| Squarepoint Ops LLC new | 44,626 | $402K | 0.1% | 2026-Q1 |
| ALPS ADVISORS INC trimmed | 43,992 | $396K | 0.1% | 2026-Q1 |
| STATE OF WISCONSIN INVESTMENT BOARD new | 41,671 | $375K | 0.1% | 2026-Q1 |
| RHUMBLINE ADVISERS trimmed | 41,203 | $371K | 0.1% | 2026-Q1 |
| Invesco Ltd. trimmed | 40,510 | $365K | 0.1% | 2026-Q1 |
| CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM added | 39,661 | $357K | 0.1% | 2026-Q1 |
| GSA CAPITAL PARTNERS LLP new | 39,232 | $353K | 0.1% | 2026-Q1 |
| Stonepine Capital Management, LLC new | 35,000 | $315K | 0.0% | 2026-Q1 |
| VANGUARD GROUP INC trimmed | 2,133,212 | $58M | 8.5% | 2025-Q4 stale |
| JANUS HENDERSON GROUP PLC new | 1,527,958 | $41M | 6.1% | 2025-Q4 stale |
| Omega Fund Management, LLC trimmed | 1,326,293 | $36M | 5.3% | 2025-Q4 stale |
| VR ADVISER, LLC | 1,169,298 | $32M | 4.7% | 2025-Q4 stale |
| Integral Health Asset Management, LLC added | 750,000 | $20M | 3.0% | 2025-Q4 stale |
| Vestal Point Capital, LP new | 720,000 | $20M | 2.9% | 2025-Q4 stale |
| Siren, L.L.C. trimmed | 588,450 | $16M | 2.3% | 2025-Q4 stale |
| Deep Track Capital, LP trimmed | 1,442,767 | $16M | 2.3% | 2025-Q2 stale |
| GREAT POINT PARTNERS LLC | 300,000 | $8M | 1.2% | 2025-Q4 stale |
| JENNISON ASSOCIATES LLC new | 288,847 | $8M | 1.2% | 2025-Q4 stale |
| Squadron Capital Management LLC new | 230,650 | $6M | 0.9% | 2025-Q4 stale |
| SummitTX Capital, L.P. added | 116,724 | $3M | 0.5% | 2025-Q4 stale |
| Ikarian Capital, LLC new | 161,113 | $3M | 0.4% | 2025-Q3 stale |
| Lynx1 Capital Management LP | 219,247 | $2M | 0.4% | 2025-Q2 stale |
| Artia Global Partners LP new | 68,653 | $2M | 0.3% | 2025-Q4 stale |
| Exome Asset Management LLC added | 64,845 | $2M | 0.3% | 2025-Q4 stale |
| AMERIPRISE FINANCIAL INC new | 56,557 | $2M | 0.2% | 2025-Q4 stale |
| BALYASNY ASSET MANAGEMENT L.P. trimmed | 73,131 | $1M | 0.2% | 2025-Q3 stale |
| SEVEN GRAND MANAGERS, LLC new | 50,000 | $1M | 0.2% | 2025-Q4 stale |
| Velan Capital Investment Management LP | 107,000 | $1M | 0.2% | 2025-Q2 stale |
| BOOTHBAY FUND MANAGEMENT, LLC new | 61,299 | $1M | 0.2% | 2025-Q3 stale |
| Rafferty Asset Management, LLC added | 38,683 | $1M | 0.2% | 2025-Q4 stale |
| NOMURA HOLDINGS INC new | 28,290 | $532K | 0.1% | 2025-Q3 stale |
| PSP Research LLC new | 17,634 | $479K | 0.1% | 2025-Q4 stale |
| PRELUDE CAPITAL MANAGEMENT, LLC added | 16,560 | $450K | 0.1% | 2025-Q4 stale |
| PROFUND ADVISORS LLC new | 14,582 | $396K | 0.1% | 2025-Q4 stale |
| Graham Capital Management, L.P. new | 13,712 | $372K | 0.1% | 2025-Q4 stale |
| EcoR1 Capital, LLC | 60,000 | $367K | 0.1% | 2025-Q1 stale |
| CITADEL ADVISORS LLC trimmed | 13,420 | $364K | 0.1% | 2025-Q4 stale |
| Caption Management, LLC new | 18,196 | $342K | 0.1% | 2025-Q3 stale |
| Virtu Financial LLC new | 12,246 | $332K | 0.0% | 2025-Q4 stale |
| Verition Fund Management LLC trimmed | 12,020 | $326K | 0.0% | 2025-Q4 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.