As of November 7, 2026, 3 holders' latest Schedule 13D or 13G filings report owning 5% or more of Acumen Pharmaceuticals, Inc. The largest reported stake is RA Capital Management, L.P.'s, at 29.5%. 4 filings are on record since August 13, 2025 (Schedule 13D/A, March 17, 2026).
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Key facts
- · Reporting person: James B. Murray Jr. · Sole voting: 3,468,465 · Shared voting: 142,895 · Sole dispositive: 3,468,465 · Shared dispositive: 142,895 · SCHEDULE 13G, 2026-04-07
- · Reporting person: RA Capital Management, L.P. · Sole voting: 0 · Shared voting: 21,101,669 · Sole dispositive: 0 · Shared dispositive: 21,101,669 · SCHEDULE 13D/A, 2026-03-17
- · Reporting person: Franklin Resources, Inc. · Sole voting: 2,305,096 · Shared voting: 0 · Sole dispositive: 2,305,096 · Shared dispositive: 0 · SCHEDULE 13G/A, 2025-11-04
- · Reporting person: Sands Capital Alternatives, LLC · Sole voting: 0 · Shared voting: 3,417,075 · Sole dispositive: 0 · Shared dispositive: 3,417,075 · SCHEDULE 13G/A, 2025-08-13
Acumen Pharmaceuticals, Inc. has 4 Schedule 13D or 13G filings on record since 2025-08-13. 3 holders' latest filing reports 5% or more of common stock, $0.0001 par value per share. Each figure below is the holder's own, as filed, with the filing linked.
Layoffs on record: about 52 jobs, latest 2026-11-05 (layoff filings and notices).
Holders
| Holder | Percent | Shares | Latest | Event date |
|---|---|---|---|---|
| RA Capital Management, L.P. | 29.5% | 21,101,669 | SCHEDULE 13D/A, 2026-03-17 | 2026-03-13 |
| Sands Capital Alternatives, LLC | 5.6% | 3,417,075 | SCHEDULE 13G/A, 2025-08-13 | 2025-06-30 |
| 5% | 3,611,360 | SCHEDULE 13G, 2026-04-07 | 2025-04-04 | |
| Franklin Resources, Inc. | 3.8% | 2,305,096 | SCHEDULE 13G/A, 2025-11-04 | 2025-09-30 |
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More on Acumen Pharmaceuticals, Inc. and the records around it.
Acumen Pharmaceuticals, Inc. elsewhere on the record
Companies that share a holder
- Franklin Resources, Inc. also filed stake reports on 41 other companies: Adicet Bio, Inc. (Oct 2026), ALBEMARLE CORPORATION (Oct 2026), Andersen Group Inc. (Oct 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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What the Full Report on Acumen Pharmaceuticals, Inc. covers
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Voting and dispositive power, as filed
| Reporting person | Sole voting | Shared voting | Sole dispositive | Shared dispositive | Filing |
|---|---|---|---|---|---|
| RA Capital Management, L.P. | 0 | 21,101,669 | 0 | 21,101,669 | SCHEDULE 13D/A, 2026-03-17 |
| Peter Kolchinsky | 0 | 21,101,669 | 0 | 21,101,669 | SCHEDULE 13D/A, 2026-03-17 |
| Rajeev Shah | 0 | 21,101,669 | 0 | 21,101,669 | SCHEDULE 13D/A, 2026-03-17 |
| RA Capital Healthcare Fund, L.P. | 0 | 19,103,785 | 0 | 19,103,785 | SCHEDULE 13D/A, 2026-03-17 |
| Sands Capital Alternatives, LLC | 0 | 3,417,075 | 0 | 3,417,075 | SCHEDULE 13G/A, 2025-08-13 |
| Sands Capital Ventures Discovery Fund III, L.P. | 0 | 1,124,729 | 0 | 1,124,729 | SCHEDULE 13G/A, 2025-08-13 |
| Sands Capital Global Venture Fund II, L.P. | 0 | 1,146,173 | 0 | 1,146,173 | SCHEDULE 13G/A, 2025-08-13 |
| Sands Capital Life Sciences Pulse Fund, LLC | 0 | 1,146,173 | 0 | 1,146,173 | SCHEDULE 13G/A, 2025-08-13 |
| Sands Frank M. | 0 | 3,417,075 | 0 | 3,417,075 | SCHEDULE 13G/A, 2025-08-13 |
| James B. Murray Jr. | 3,468,465 | 142,895 | 3,468,465 | 142,895 | SCHEDULE 13G, 2026-04-07 |
| Franklin Resources, Inc. | 2,305,096 | 0 | 2,305,096 | 0 | SCHEDULE 13G/A, 2025-11-04 |
| Charles B. Johnson | 0 | 0 | 0 | 0 | SCHEDULE 13G/A, 2025-11-04 |
| Rupert H. Johnson, Jr. | 0 | 0 | 0 | 0 | SCHEDULE 13G/A, 2025-11-04 |
The latest filing identifies Acumen Pharmaceuticals, Inc. by CUSIP 00509G209 and gives its principal executive office as 1210-1220 Washington Street, Suite 210, Newton, MA 02465 (SCHEDULE 13G, 2026-04-07).
What the percentages are based on
Percent of Common Stock and total voting power of the Issuer's Common Stock is based on the denominator of 72,212,758 shares of the Issuer's Common Stock outstanding as of March 20, 2026, as disclosed in the Issuer's Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 26, 2026. Based on the above, as of April 6, 2026, Mr.James B. Murray Jr., SCHEDULE 13G, 2026-04-07
Source of funds (Item 3)
Item 3 of the Statement is hereby amended and supplemented as follows: March 2026 Securities Purchase Agreement On March 13, 2026, the Issuer entered into a securities purchase agreement (the "March 2026 Securities Purchase Agreement") with certain institutional accredited investors (the "March 2026 PIPE Investors"), including the Fund, pursuant to which the Issuer agreed to issue and sell to the March 2026 PIPE Investors in a private placement (the "March 2026 Private Placement") an aggregate of 10,833,331 shares of common stock (the "Shares") at a price of $3.30 per share.RA Capital Management, L.P., SCHEDULE 13D/A, 2026-03-17
Timeline
| Filed | Holder | Percent | Filing |
|---|---|---|---|
| 2025-08-13 | Sands Capital Alternatives, LLC | 5.6% | SCHEDULE 13G/A |
| 2025-11-04 | Franklin Resources, Inc. | 3.8% | SCHEDULE 13G/A |
| 2026-03-17 | RA Capital Management, L.P. | 29.5% | SCHEDULE 13D/A |
| 2026-04-07 | James B. Murray Jr. | 5% | SCHEDULE 13G |
Questions about who owns Acumen Pharmaceuticals, Inc.
Who owns Acumen Pharmaceuticals, Inc.?
On this page, 3 holders' latest ownership filings report 5% or more of Acumen Pharmaceuticals, Inc.: RA Capital Management, L.P. (29.5%, Schedule 13D/A, filed 2026-03-17), Sands Capital Alternatives, LLC (5.6%, Schedule 13G/A, filed 2025-08-13) and James B. Murray Jr. (5%, Schedule 13G, filed 2026-04-07).
Who are the largest shareholders of Acumen Pharmaceuticals, Inc.?
By the share each holder's latest filing reports, the largest holders of Acumen Pharmaceuticals, Inc. on this page are RA Capital Management, L.P. (29.5%), Sands Capital Alternatives, LLC (5.6%) and James B. Murray Jr. (5%).
When did RA Capital Management, L.P. buy into Acumen Pharmaceuticals, Inc.?
The filings give report dates, not purchase dates. The earliest filing from RA Capital Management, L.P. on this page is the Schedule 13D/A, filed 2026-03-17, reporting 29.5%. 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%); 4 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.
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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.