Who owns Seres Therapeutics (MCRB)
Which tracked institutional funds hold MCRB, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See MCRB 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 MCRB is one-sided between 2026-Q1 and 2026-Q2: 1 added or opened and 5 trimmed or exited — on balance reducing.
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
MCRB’s largest tracked holder by dollar value, Flagship Pioneering, LLC, sizes it at 0.6% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 0.6pp conviction gap — its largest holder concentrates the name more heavily than the typical one.
Book-share is each fund’s reported value in MCRB 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 36 tracked filers holding MCRB, 15 increased or opened the position and 17 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 MCRB 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.
Largest adds
- MARSHALL WACE, LLP$255K
Largest trims
- Flagship Pioneering, LLC$1M
- SUSQUEHANNA INTERNATIONAL GROUP, LLP$474K
- VANGUARD CAPITAL MANAGEMENT LLC$338K
- AMERICAN CENTURY COMPANIES INC$329K
- Vontobel Holding Ltd.$258K
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 |
|---|---|---|---|---|
| Flagship Pioneering, LLC | 1,155,850 | $9M | 34.3% | 2026-Q2 |
| VANGUARD CAPITAL MANAGEMENT LLC trimmed | 287,776 | $2M | 8.5% | 2026-Q2 |
| MARSHALL WACE, LLP added | 172,245 | $1M | 5.1% | 2026-Q2 |
| Vontobel Holding Ltd. trimmed | 122,975 | $970K | 3.6% | 2026-Q2 |
| BlackRock, Inc. added | 111,000 | $876K | 3.3% | 2026-Q2 |
| GEODE CAPITAL MANAGEMENT, LLC added | 79,974 | $631K | 2.4% | 2026-Q2 |
| SUSQUEHANNA INTERNATIONAL GROUP, LLP trimmed | 58,328 | $460K | 1.7% | 2026-Q2 |
| VANGUARD FIDUCIARY TRUST CO added | 48,685 | $384K | 1.4% | 2026-Q2 |
| STATE STREET CORP | 33,901 | $267K | 1.0% | 2026-Q2 |
| Lion Point Capital, LP | 31,570 | $249K | 0.9% | 2026-Q2 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 31,049 | $245K | 0.9% | 2026-Q2 |
| AMERICAN CENTURY COMPANIES INC trimmed | 28,313 | $223K | 0.8% | 2026-Q2 |
| XTX Topco Ltd trimmed | 20,732 | $164K | 0.6% | 2026-Q2 |
| GOLDMAN SACHS GROUP INC added | 15,229 | $120K | 0.5% | 2026-Q2 |
| NORTHERN TRUST CORP | 14,765 | $116K | 0.4% | 2026-Q2 |
| Invesco Ltd. trimmed | 12,974 | $102K | 0.4% | 2026-Q2 |
| MORGAN STANLEY trimmed | 12,138 | $96K | 0.4% | 2026-Q2 |
| CITADEL ADVISORS LLC trimmed | 10,504 | $83K | 0.3% | 2026-Q2 |
| SIMPLEX TRADING, LLC added | 4,598 | $36K | 0.1% | 2026-Q2 |
| SBI Securities Co., Ltd. added | 4,182 | $33K | 0.1% | 2026-Q2 |
| Integrated Wealth Concepts LLC trimmed | 4,000 | $32K | 0.1% | 2026-Q2 |
| GROUP ONE TRADING LLC added | 3,714 | $29K | 0.1% | 2026-Q2 |
| JPMORGAN CHASE & CO added | 3,636 | $28K | 0.1% | 2026-Q2 |
| Vanguard Global Advisers, LLC | 1,975 | $16K | 0.1% | 2026-Q2 |
| FMR LLC trimmed | 1,528 | $12K | 0.0% | 2026-Q2 |
| Rachor Investment Advisory Services, LLC | 1,477 | $12K | 0.0% | 2026-Q2 |
| UBS Group AG trimmed | 484 | $4K | 0.0% | 2026-Q2 |
| Tower Research Capital LLC (TRC) trimmed | 316 | $2K | 0.0% | 2026-Q2 |
| BNP PARIBAS FINANCIAL MARKETS | 211 | $2K | 0.0% | 2026-Q2 |
| BARCLAYS PLC trimmed | 167 | $1K | 0.0% | 2026-Q2 |
| Continuum Advisory, LLC trimmed | 47 | $371 | 0.0% | 2026-Q2 |
| WELLS FARGO & COMPANY/MN | 10 | $79 | 0.0% | 2026-Q2 |
| OSAIC HOLDINGS, INC. | 8 | $63 | 0.0% | 2026-Q2 |
| Larson Financial Group LLC trimmed | 5 | $39 | 0.0% | 2026-Q2 |
| WHITTIER TRUST CO OF NEVADA INC new | 1 | $8 | 0.0% | 2026-Q2 |
| ROYAL BANK OF CANADA trimmed | 11 | — | 0.0% | 2026-Q2 |
| TWO SIGMA INVESTMENTS, LP trimmed | 18,794 | $167K | 0.6% | 2026-Q1 stale (1 quarter behind) |
| Physician Wealth Advisors, Inc. | 142 | $1K | 0.0% | 2026-Q1 stale (1 quarter behind) |
| Sound Income Strategies, LLC | 8 | $71 | 0.0% | 2026-Q1 stale (1 quarter behind) |
| Allworth Financial LP | 4 | $36 | 0.0% | 2026-Q1 stale (1 quarter behind) |
| Arax Advisory Partners added | 6 | $18 | 0.0% | 2026-Q1 stale (1 quarter behind) |
| VANGUARD GROUP INC added | 324,214 | $5M | 18.1% | 2025-Q4 stale (2 quarters behind) |
| HRT FINANCIAL LP added | 62,900 | $935K | 3.5% | 2025-Q4 stale (2 quarters behind) |
| 683 Capital Management, LLC new | 52,314 | $778K | 2.9% | 2025-Q4 stale (2 quarters behind) |
| Schonfeld Strategic Advisors LLC added | 29,097 | $433K | 1.6% | 2025-Q4 stale (2 quarters behind) |
| OMERS ADMINISTRATION Corp new | 14,400 | $214K | 0.8% | 2025-Q4 stale (2 quarters behind) |
| ExodusPoint Capital Management, LP new | 12,737 | $190K | 0.7% | 2025-Q4 stale (2 quarters behind) |
| BANK OF AMERICA CORP /DE/ trimmed | 195 | $3K | 0.0% | 2025-Q4 stale (2 quarters behind) |
| J. Goldman & Co LP new | 27,000 | $519K | 2.0% | 2025-Q3 stale (3 quarters behind) |
| CITIGROUP INC added | 2,621 | $50K | 0.2% | 2025-Q3 stale (3 quarters behind) |
| US BANCORP \DE\ trimmed | 12 | $231 | 0.0% | 2025-Q3 stale (3 quarters behind) |
| Federation des caisses Desjardins du Quebec new | 3 | $58 | 0.0% | 2025-Q3 stale (3 quarters behind) |
| Squarepoint Ops LLC trimmed | 20,908 | $232K | 0.9% | 2025-Q2 stale (4 quarters behind) |
| TANG CAPITAL MANAGEMENT LLC trimmed | 13,921 | $155K | 0.6% | 2025-Q2 stale (4 quarters behind) |
| BRIDGEWAY CAPITAL MANAGEMENT, LLC trimmed | 12,500 | $139K | 0.5% | 2025-Q2 stale (4 quarters behind) |
| Atlantic Union Bankshares Corp new | 411 | $5K | 0.0% | 2025-Q2 stale (4 quarters behind) |
| RAYMOND JAMES FINANCIAL INC new | 56 | $623 | 0.0% | 2025-Q2 stale (4 quarters behind) |
1 parent filing withheld from the table above, and from the coverage figures, to avoid listing one book twice: WHITTIER TRUST CO (last filed 2025-Q2, 1 shares) reconciles to its 1 current affiliate (1 shares) — 0.000% apart.
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.