As of November 6, 2026, 2 holders' latest Schedule 13D or 13G filings report owning 5% or more of Day One Biopharmaceuticals, Inc. The largest reported stake is BlackRock, Inc.'s, at 5.8%. 13 filings are on record since July 17, 2025 (Schedule 13G, July 17, 2025).
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Key facts
- · Holder: Vestal Point Capital, LP · Percent: 0% · SCHEDULE 13G/A
- · Holder: Atlas Venture Fund XI, L.P. · Percent: 0% · SCHEDULE 13G/A
- · Holder: AI Day1 LLC · Percent: 0% · SCHEDULE 13D/A
- · Holder: AI Day1 LLC · Percent: 12.52% · SCHEDULE 13D/A
- · Holder: Fmr LLC · Percent: 0% · SCHEDULE 13G/A
Day One Biopharmaceuticals, Inc. has 13 Schedule 13D or 13G filings on record since 2025-07-17. 2 holders' latest filing reports 5% or more of common stock, par value $0.0001 per share. Each figure below is the holder's own, as filed, with the filing linked.
Holders
| Holder | Percent | Shares | Latest | Event date |
|---|---|---|---|---|
| BlackRock, Inc. | 5.8% | 5,849,917 | SCHEDULE 13G, 2025-07-17 | 2025-06-30 |
| Glazer Capital, LLC | 5.4% | 5,615,390 | SCHEDULE 13G, 2026-03-19 | 2026-03-12 |
| Fmr LLC | 0% | 23,640 | SCHEDULE 13G/A, 2026-04-07 | 2026-03-31 |
| RA Capital Management, L.P. | 0% | 0 | SCHEDULE 13G/A, 2025-08-14 | 2025-06-30 |
| Vestal Point Capital, LP | 0% | 0 | SCHEDULE 13G/A, 2026-05-15 | 2026-03-31 |
| The Vanguard Group | 0% | 0 | SCHEDULE 13G/A, 2026-03-26 | 2026-03-13 |
| AI Day1 LLC | 0% | 0 | SCHEDULE 13D/A, 2026-04-27 | 2026-04-23 |
| Atlas Venture Fund XI, L.P. | 0% | 0 | SCHEDULE 13G/A, 2026-05-14 | 2026-03-31 |
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More on Day One Biopharmaceuticals, Inc. and the records around it.
Companies that share a holder
- Atlas Venture Fund XI, L.P. also filed stake reports on 3 other companies: DYNE THERAPEUTICS, INC. (Aug 2026), Korro Bio, Inc. (Aug 2026), SIONNA THERAPEUTICS, INC. (Oct 2025)
- Vestal Point Capital, LP also filed stake reports on 27 other companies: Alto Neuroscience, Inc. (Aug 2026), iBio, Inc. (Aug 2026), Immunocore Holdings plc (Aug 2026)
- RA Capital Management, L.P. also filed stake reports on 100 other companies: Climb Bio, Inc. (Nov 2026), Bambusa Therapeutics, Inc. (Nov 2026), SOLID BIOSCIENCES INC. (Nov 2026)
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Example from a real report (our sample on Target): “The Q2 2026 earnings report, published August 19, 2026, showed adjusted EPS of $2.46 against an expected $2.33” Source: CNBC
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What the Full Report on Day One Biopharmaceuticals, Inc. covers
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Who Pays Them, And Who They Are Up Against
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Purpose of Transaction (Item 4)
AI Day1 LLC
The disclosure in Item 4 is hereby amended and supplemented by adding the following at the end thereof: On April 9, 2026, AI Day1 tendered all of its shares of Common Stock pursuant to the tender offer by Servier Detroit Inc. ("Purchaser") to purchase all of the issued and outstanding shares of Common Stock for $21.50 per share in cash, upon the terms and subject to the conditions described in the Offer to Purchase and related Letter of Transmittal filed with the SEC on Schedule TO on March 26, 2026 (the "Tender Offer"). Such shares were accepted by the Purchaser on April 23, 2026. On April 23, 2026, in connection with the consummation of the merger, each pre-funded warrant held by AI Day1 to purchase Common Stock was converted into the right to receive $21.4999 per warrant in cash.Item 4 of the SCHEDULE 13D/A filed 2026-04-27
Timeline
| Filed | Holder | Percent | Filing |
|---|---|---|---|
| 2025-07-17 | BlackRock, Inc. | 5.8% | SCHEDULE 13G |
| 2025-08-06 | Fmr LLC | 11.2% | SCHEDULE 13G/A |
| 2025-08-14 | RA Capital Management, L.P. | 0% | SCHEDULE 13G/A |
| 2025-11-05 | Fmr LLC | 9.9% | SCHEDULE 13G/A |
| 2026-02-05 | Fmr LLC | 5.6% | SCHEDULE 13G/A |
| 2026-02-17 | Vestal Point Capital, LP | 5.1% | SCHEDULE 13G |
| 2026-03-19 | Glazer Capital, LLC | 5.4% | SCHEDULE 13G |
| 2026-03-26 | The Vanguard Group | 0% | SCHEDULE 13G/A |
| 2026-04-07 | Fmr LLC | 0% | SCHEDULE 13G/A |
| 2026-04-13 | AI Day1 LLC | 12.52% | SCHEDULE 13D/A |
| 2026-04-27 | AI Day1 LLC | 0% | SCHEDULE 13D/A |
| 2026-05-14 | Atlas Venture Fund XI, L.P. | 0% | SCHEDULE 13G/A |
| 2026-05-15 | Vestal Point Capital, LP | 0% | SCHEDULE 13G/A |
Questions about who owns Day One Biopharmaceuticals, Inc.
Who owns Day One Biopharmaceuticals, Inc.?
On this page, 2 holders' latest ownership filings report 5% or more of Day One Biopharmaceuticals, Inc.: BlackRock, Inc. (5.8%, Schedule 13G, filed 2025-07-17) and Glazer Capital, LLC (5.4%, Schedule 13G, filed 2026-03-19).
Who are the largest shareholders of Day One Biopharmaceuticals, Inc.?
By the share each holder's latest filing reports, the largest holders of Day One Biopharmaceuticals, Inc. on this page are BlackRock, Inc. (5.8%) and Glazer Capital, LLC (5.4%).
When did BlackRock, Inc. buy into Day One Biopharmaceuticals, Inc.?
The filings give report dates, not purchase dates. The earliest filing from BlackRock, Inc. on this page is the Schedule 13G, filed 2025-07-17, reporting 5.8%.
Is this an audit or a full list?
Neither. The ownership list on this page covers only Schedule 13D and 13G filings, which holders make once they own 5% or more of a class of shares (an amendment can report a stake that has since fallen below 5%); 13 such filings are shown here. It is not an audit and not a full cap table: holders who never reached 5% are not listed, and a stake can change after its latest filing.
Also on the record for Day One Biopharmaceuticals, Inc.
| Date | Record | Figure | Our page | Source |
|---|---|---|---|---|
| April 23, 2026 | Leadership change filing (Form 8-K, Item 5.02) | — | Leadership changes | Source |
| January 6, 2026 | Acquired Mersana Therapeutics, Inc. | $128.80M | Acquisition | Source |
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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.