Boundless Bio, Inc.: 5%+ holders

As of November 6, 2026, 4 holders' latest Schedule 13D or 13G filings report owning 5% or more of Boundless Bio, Inc. The largest reported stake is Fmr LLC's, at 12%. 8 filings are on record since August 14, 2025 (Schedule 13G/A, February 5, 2026).

ADAR1 Capital Management, LLC also filed stake reports on 29 other companies ↓

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Key facts

• Filing 2026-08-27 · Reporting person: Zachary Hornby · Sole voting: 2,426,857 · Shared voting: 0 · Sole dispositive: 2,426,857 · Shared dispositive: 0 · SCHEDULE 13G, 2026-08-27
• Filing 2026-08-14 · Reporting person: ADAR1 Capital Management, LLC · Sole voting: 0 · Shared voting: 1,968,216 · Sole dispositive: 0 · Shared dispositive: 1,968,216 · SCHEDULE 13G, 2026-08-14
• Filing 2026-08-14 · Reporting person: Citadel Advisors LLC · Sole voting: 0 · Shared voting: 0 · Sole dispositive: 0 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-08-14
• Filing 2026-06-29 · Reporting person: Tang Capital Management, LLC · Sole voting: 0 · Shared voting: 2,533,845 · Sole dispositive: 0 · Shared dispositive: 2,533,845 · SCHEDULE 13G, 2026-06-29
• Filed 2026-02-17 · Holder: Nextech VI GP S.a. r.l. · Percent: 0% · SCHEDULE 13G/A

Boundless Bio, Inc. has 8 Schedule 13D or 13G filings on record since 2025-08-14. 4 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.

Layoffs on record: 1 filing or notice, latest 2026-06-23 (layoff filings and notices).

Holders

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More on Boundless Bio, Inc. and the records around it.

Boundless Bio, Inc. elsewhere on the record

• Layoff notices Jun 2026
• Who owns it

Companies that share a holder

• ADAR1 Capital Management, LLC also filed stake reports on 29 other companies: InMed Pharmaceuticals, Inc. (Oct 2026), Tenax Therapeutics, Inc. (Sep 2026), Adagio Medical Holdings, Inc. (Aug 2026)
• TANG CAPITAL MANAGEMENT, LLC also filed stake reports on 33 other companies: EyePoint, Inc. (Oct 2026), Skye Bioscience, Inc. (Oct 2026), Nano Dimension Ltd. (Aug 2026)
• Citadel Advisors LLC also filed stake reports on 58 other companies: Quantinuum Inc. (Oct 2026), REALLOYS INC. (Oct 2026), STARFIGHTERS SPACE, INC. (Oct 2026)

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Voting and dispositive power, as filed

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The latest filing identifies Boundless Bio, Inc. by CUSIP 10170A100 and gives its principal executive office as 11099 North Torrey Pines Road, Suite 150, La Jolla, CA 92037 (SCHEDULE 13G, 2026-08-27).

Timeline

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Questions about who owns Boundless Bio, Inc.

Who owns Boundless Bio, Inc.?

On this page, 4 holders' latest ownership filings report 5% or more of Boundless Bio, Inc.: Fmr LLC (12%, Schedule 13G/A, filed 2026-02-05), Tang Capital Management, LLC (11.3%, Schedule 13G, filed 2026-06-29), Zachary Hornby (9.8%, Schedule 13G, filed 2026-08-27) and ADAR1 Capital Management, LLC (8.8%, Schedule 13G, filed 2026-08-14).

Who are the largest shareholders of Boundless Bio, Inc.?

By the share each holder's latest filing reports, the largest holders of Boundless Bio, Inc. on this page are Fmr LLC (12%), Tang Capital Management, LLC (11.3%) and Zachary Hornby (9.8%).

When did Fmr LLC buy into Boundless Bio, Inc.?

The filings give report dates, not purchase dates. The earliest filing from Fmr LLC on this page is the Schedule 13G/A, filed 2026-02-05, reporting 12%. That earliest filing is itself an amendment, which updates an earlier report.

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%); 8 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 Boundless Bio, Inc.

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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.

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