Generation Bio Co. has 12 Schedule 13D or 13G filings on record since 2025-07-17. 1 holder's latest filing reports 5% or more of common stock, $0.0001 par value. Each figure below is the holder's own, as filed, with the filing linked.
Holders
| Holder | Percent | Shares | Latest | Event date |
|---|---|---|---|---|
| SymBiosis Capital Partners, LLC | 6.3% | 421,926 | SCHEDULE 13G/A, 2025-11-14 | 2025-09-30 |
| Renaissance Technologies LLC | 4.27% | 287,614 | SCHEDULE 13G/A, 2026-02-12 | 2025-12-31 |
| Fmr LLC | 3.5% | 2,345,624 | SCHEDULE 13G/A, 2025-08-06 | 2025-06-30 |
| T. Rowe Price Associates, Inc. | 3.1% | 209,641 | SCHEDULE 13G/A, 2026-02-17 | 2025-12-31 |
| BlackRock, Inc. | 1.7% | 1,152,047 | SCHEDULE 13G/A, 2025-07-17 | 2025-06-30 |
| Baselake Partners, LP | 0% | 0 | SCHEDULE 13G/A, 2026-02-11 | 2026-02-09 |
| Atlas Venture Fund X, L.P. | 0% | 0 | SCHEDULE 13G/A, 2026-05-14 | 2026-03-31 |
Timeline
| Filed | Holder | Percent | Filing |
|---|---|---|---|
| 2025-07-17 | BlackRock, Inc. | 1.7% | SCHEDULE 13G/A |
| 2025-08-06 | Fmr LLC | 3.5% | SCHEDULE 13G/A |
| 2025-08-14 | T. Rowe Price Associates, Inc. | 12.6% | SCHEDULE 13G/A |
| 2025-11-13 | Renaissance Technologies LLC | 5.11% | SCHEDULE 13G |
| 2025-11-14 | T. Rowe Price Associates, Inc. | 8.6% | SCHEDULE 13G/A |
| 2025-11-14 | SymBiosis Capital Partners, LLC | 6.3% | SCHEDULE 13G |
| 2025-11-14 | SymBiosis Capital Partners, LLC | 6.3% | SCHEDULE 13G/A |
| 2026-02-06 | Baselake Partners, LP | 5.2% | SCHEDULE 13G |
| 2026-02-11 | Baselake Partners, LP | 0% | SCHEDULE 13G/A |
| 2026-02-12 | Renaissance Technologies LLC | 4.27% | SCHEDULE 13G/A |
| 2026-02-17 | T. Rowe Price Associates, Inc. | 3.1% | SCHEDULE 13G/A |
| 2026-05-14 | Atlas Venture Fund X, L.P. | 0% | SCHEDULE 13G/A |
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Where this comes from
Anyone who comes to own more than 5% of a class of a listed company's voting shares has to tell the SEC. A holder who may seek to change or influence the company files Schedule 13D, and has to say in Item 4, "Purpose of Transaction", what it intends to do. A holder with no such intent, such as many index and passive funds, may file the shorter Schedule 13G. Both are amended when the stake changes, including when it falls below 5%.
Every row here is one of those filings, linked to the filing itself. Percentages and share counts are exactly as the holder filed them, for the holder the filing names; an amendment showing a lower figure is shown as filed. Item 4 text is quoted word for word. Where a 13D's Item 4 contains a sentence stating a definite intent to influence the company, that sentence is marked and quoted; the page does not describe the holder or its motives beyond the words it filed. Nothing here is investment advice.