X4 Pharmaceuticals Inc: 5%+ holders

As of November 7, 2026, 11 holders' latest Schedule 13D or 13G filings report owning 5% or more of X4 Pharmaceuticals Inc. The largest reported stake is Morgan Stanley's, at 10.2%. 30 filings are on record since July 18, 2025 (Schedule 13G/A, March 6, 2026).

Bain Capital Life Sciences Fund, L.P. also filed stake reports on 2 other companies ↓

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Key facts

• Filing 2026-10-07 · Reporting person: Fmr LLC · Sole voting: 4,558,586 · Shared voting: 0 · Sole dispositive: 4,558,616 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-10-07
• Filing 2026-09-21 · Reporting person: Venrock Healthcare Capital Partners III, L.P. · Sole voting: 0 · Shared voting: 5,555,047 · Sole dispositive: 0 · Shared dispositive: 5,555,047 · SCHEDULE 13G, 2026-09-21
• Filing 2026-08-14 · Reporting person: Deep Track Capital, LP · Sole voting: 0 · Shared voting: 8,040,894 · Sole dispositive: 0 · Shared dispositive: 8,040,894 · SCHEDULE 13G/A, 2026-08-14
• Filing 2026-08-14 · Reporting person: Perceptive Advisors LLC · Sole voting: 0 · Shared voting: 8,085,006 · Sole dispositive: 0 · Shared dispositive: 8,085,006 · SCHEDULE 13G/A, 2026-08-14
• Filing 2026-07-30 · Reporting person: BlackRock, Inc. · Sole voting: 5,467,295 · Shared voting: 0 · Sole dispositive: 5,529,573 · Shared dispositive: 0 · SCHEDULE 13G, 2026-07-30

X4 Pharmaceuticals Inc has 30 Schedule 13D or 13G filings on record since 2025-07-18. 11 holders' latest filing reports 5% or more of common stock. Each figure below is the holder's own, as filed, with the filing linked.

Holders

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More on X4 Pharmaceuticals Inc and the records around it.

X4 Pharmaceuticals Inc elsewhere on the record

• Leadership changes Jul 2026
• Form D filing Aug 2025
• Who owns it

Companies that share a holder

• Bain Capital Life Sciences Fund, L.P. also filed stake reports on 2 other companies: Rapid Micro Biosystems, Inc. (Aug 2026), Pharvaris N.V. (Feb 2026)
• Growth Equity Opportunities 18 VGE, LLC also filed stake reports on 2 other companies: Celcuity Inc. (Mar 2026), Gossamer Bio, Inc. (Feb 2026)
• Saturn V Capital Management LP also filed stake reports on 2 other companies: Monopar Therapeutics (Aug 2026), Immix Biopharma, Inc. (Feb 2026)

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What the Full Report on X4 Pharmaceuticals Inc covers

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5. The Money: Funding, Valuation, Runway

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Voting and dispositive power, as filed

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The latest filing identifies X4 Pharmaceuticals Inc by CUSIP 98420X202 and gives its principal executive office as 61 NORTH BEACON STREET, 4TH FLOOR, BOSTON, MA 02134 (SCHEDULE 13G/A, 2026-10-07).

What the percentages are based on

Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentage of the shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.Venrock Healthcare Capital Partners III, L.P., SCHEDULE 13G, 2026-09-21

Purpose of Transaction (Item 4)

Growth Equity Opportunities 18 VGE, LLC

GEO acquired the GEO Shares for investment purposes. Information with respect to the Offering set forth in Item 3 above is incorporated herein by reference to the extent responsive to this Item 4. Subject to the foregoing, depending on market conditions, its continuing evaluation of the business and prospects of the Issuer and other factors, GEO and other Reporting Persons may dispose of or acquire additional shares of the Issuer. Except as set forth above, none of the Reporting Persons has any present plans which relate to or would result in: (a) The acquisition by any person of additional securities of the Issuer, or the disposition of securities of the Issuer; (b) An extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries; (c) A sale or transfer of a material amount of assets of the Issuer or any of its subsidiaries; (d) Any change in the present board of directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board; (e) Any material change in the present capitalization or dividend policy of the Issuer; (f) Any other material change in the Issuer's business or corporate structure; (g) Changes in the Issuer's charter, bylaws or instruments corresponding thereto or other actions which may impede the acquisition of control of the Issuer by any person; (h) Causing a class of securities of the …The first part of Item 4 of the SCHEDULE 13D/A filed 2025-10-29; the filing has the rest

Timeline

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Questions about who owns X4 Pharmaceuticals Inc

Who owns X4 Pharmaceuticals Inc?

On this page, 11 holders' latest ownership filings report 5% or more of X4 Pharmaceuticals Inc: Morgan Stanley (10.2%, Schedule 13G/A, filed 2026-03-06), Coastlands Capital LP (9.99%, Schedule 13G, filed 2025-10-03), Empery Asset Management, LP (9.99%, Schedule 13G/A, filed 2026-01-15), Deep Track Capital, LP (8.33%, Schedule 13G/A, filed 2026-08-14) and Perceptive Advisors LLC (8.1%, Schedule 13G/A, filed 2026-08-14); 6 more are listed above.

Who are the largest shareholders of X4 Pharmaceuticals Inc?

By the share each holder's latest filing reports, the largest holders of X4 Pharmaceuticals Inc on this page are Morgan Stanley (10.2%), Coastlands Capital LP (9.99%) and Empery Asset Management, LP (9.99%).

When did Morgan Stanley buy into X4 Pharmaceuticals Inc?

The filings give report dates, not purchase dates. The earliest filing from Morgan Stanley on this page is the Schedule 13G, filed 2026-02-12, reporting 9.4%; its latest, Schedule 13G/A filed 2026-03-06, reports 10.2%.

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%); 30 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 X4 Pharmaceuticals 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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