ABOS · Acumen Pharmaceuticals, Inc. · Shareholders & Ownership

$1.98 -0.08 (-3.88%) At close · Oct 23

Russell 2000 member Rebalance outlook locked

Market Cap

$143.19M

72.32M

Volume · Oct 23 541.79K Avg daily vol (3M) 458.35K

Every disclosed holder of ABOS in one list: 13F institutions, Schedule 13D and 13G filers, insiders (Forms 3, 4 and 5) and registered funds, each from its own latest filing. Holders nest by CIK and SEC reporting links, never by name, and each is summed once.

How the holder list picks a filing →

Who Owns ABOS

13F quarter Sep 30, 2026, combined view: filers that have not filed yet carry their Jun 30, 2026 positions

Holder group	Holders	Shares	% Out	Summed
Institutional (13F)	96	47,828,085	66.14%	Yes
Insiders (Forms 3, 4, 5)	14	2,618,538	3.62%	Yes
13D/G-only blocks	1	3,611,360	4.99%	Yes
Remaining	—	18,259,302	25.25%	Rest
Registered funds (N-PORT, not summed)	68	6,044,270	8.36%	No

Shares outstanding: 72,317,285, the issuer's latest cover-page count restated onto today's split basis.

13D/G-only counts each filer's latest 13D or 13G that no 13F report of the listing contains, that names no 13F filer and that no counted insider files. Funds are never summed: their shares sit inside their advisers' 13F reports.

Holders of ABOS

One row per holder Every filing By ultimate parent

All 13F Funds Insiders 13D/G Non-US

#	Holder	Shares	% Out	Change	As of	Notes
1	RA CAPITAL MANAGEMENT, L.P. 13F CIK 1346824 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	20,992,669	29.03%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
1.1	RA CAPITAL MANAGEMENT, L.P. Insider CIK 1346824 · Jun 3, 2026 Director, issuer-wide, not summed	21,040,969	29.10%	+48,300	Jun 3, 2026	Director, issuer-wide, not summed
2	Sands Capital Alternatives, LLC 13F CIK 1846444 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	3,720,105	5.14%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
3	James B. Murray Jr. 13G CIK 1008670 · Unknown · Apr 4, 2025 Rule 13d-1(c), passive investor	3,611,360	4.99%	+930,303	Apr 4, 2025	Rule 13d-1(c), passive investor
4	BlackRock, Inc. 13F CIK 2012383 · Holding company · Jun 30, 2026 carried, not yet filed for the newest quarter	2,490,115	3.44%	+2,311,789	Jun 30, 2026	carried, not yet filed for the newest quarter
4.1	iShares Russell 2000 ETF Fund S000004344 · Registered fund · Jun 30, 2026 iShares Trust, not summed	1,036,119	1.43%	—	Jun 30, 2026	iShares Trust, not summed
4.2	iShares Russell 2000 Value ETF Fund S000004342 · Registered fund · Jun 30, 2026 iShares Trust, not summed	430,091	0.59%	—	Jun 30, 2026	iShares Trust, not summed
4.3	iShares Micro-Cap ETF Fund S000004439 · Registered fund · Jun 30, 2026 iShares Trust, not summed	158,629	0.22%	+61,510	Jun 30, 2026	iShares Trust, not summed
4.4	Master Small Cap Index Series Fund S000002716 · Registered fund · Jun 30, 2026 Quantitative Master Series LLC, not summed	88,342	0.12%	—	Jun 30, 2026	Quantitative Master Series LLC, not summed
4.5	BlackRock Small Cap Index V.I. Fund Fund S000059910 · Registered fund · Jun 30, 2026 BlackRock Variable Series Funds, Inc., not summed	6,374	0.01%	—	Jun 30, 2026	BlackRock Variable Series Funds, Inc., not summed
5	Alyeska Investment Group, L.P. 13F CIK 1453072 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	2,454,754	3.39%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
6	FRANKLIN RESOURCES INC 13F CIK 38777 · Investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	2,305,096	3.19%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
6.1	Franklin Biotechnology Discovery Fund Fund S000006882 · Registered fund · Jul 31, 2026 Franklin Strategic Series, not summed	826,400	1.14%	0	Jul 31, 2026	Franklin Strategic Series, not summed
7	ADAR1 Capital Management, LLC 13F CIK 1940272 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	2,111,334	2.92%	-45,000	Jun 30, 2026	carried, not yet filed for the newest quarter
8	VANGUARD CAPITAL MANAGEMENT LLC 13F CIK 2100119 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	1,672,072	2.31%	+165,795	Jun 30, 2026	carried, not yet filed for the newest quarter
9	Knollwood Investment Advisory, LLC 13F CIK 1999346 · Investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	1,628,510	2.25%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
10	GEODE CAPITAL MANAGEMENT, LLC 13F CIK 1214717 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	1,141,858	1.58%	+725,620	Jun 30, 2026	carried, not yet filed for the newest quarter
11	VANGUARD TOTAL STOCK MARKET INDEX FUND Fund S000002848 · Registered fund · Jun 30, 2026 VANGUARD INDEX FUNDS, not summed	1,118,322	1.55%	0	Jun 30, 2026	VANGUARD INDEX FUNDS, not summed
12	Ikarian Capital, LLC 13F CIK 1778253 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	1,053,797	1.46%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
13	Hudson Bay Capital Management LP 13F CIK 1393825 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	955,000	1.32%	-13,940	Jun 30, 2026	carried, not yet filed for the newest quarter
14	OConnell Daniel Joseph Insider CIK 1865136 · Jan 22, 2026 Director, Chief Executive Officer, issuer-wide	881,275	1.22%	-12,035	Jan 22, 2026	Director, Chief Executive Officer, issuer-wide
15	Pathstone Holdings, LLC 13F CIK 2011612 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	859,110	1.19%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
16	RENAISSANCE TECHNOLOGIES LLC 13F CIK 1037389 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	675,025	0.93%	+201,079	Jun 30, 2026	carried, not yet filed for the newest quarter
17	TWO SIGMA INVESTMENTS, LP 13F CIK 1179392 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	622,882	0.86%	+92,070	Jun 30, 2026	carried, not yet filed for the newest quarter
18	STATE STREET CORP 13F CIK 93751 · Bank · Jun 30, 2026 carried, not yet filed for the newest quarter	600,528	0.83%	+448,800	Jun 30, 2026	carried, not yet filed for the newest quarter
18.1	STATE STREET SMALL/MID CAP EQUITY INDEX PORTFOLIO Fund S000050332 · Registered fund · Jun 30, 2026 STATE STREET INSTITUTIONAL INVESTMENT TRUST, not summed	17,500	0.02%	—	Jun 30, 2026	STATE STREET INSTITUTIONAL INVESTMENT TRUST, not summed
18.2	State Street Total Return V.I.S. Fund Fund S000001637 · Registered fund · Jun 30, 2026 STATE STREET VARIABLE INSURANCE SERIES FUNDS INC, not summed	1,532	0.00%	—	Jun 30, 2026	STATE STREET VARIABLE INSURANCE SERIES FUNDS INC, not summed
19	VANGUARD EXTENDED MARKET INDEX FUND Fund S000002841 · Registered fund · Jun 30, 2026 VANGUARD INDEX FUNDS, not summed	513,511	0.71%	+157,356	Jun 30, 2026	VANGUARD INDEX FUNDS, not summed
20	NORTHERN TRUST CORP 13F CIK 73124 · Bank · Jun 30, 2026 carried, not yet filed for the newest quarter	360,744	0.50%	+285,532	Jun 30, 2026	carried, not yet filed for the newest quarter
20.1	Small Cap Index Fund Fund S000001245 · Registered fund · Jun 30, 2026 Northern Funds, not summed	24,917	0.03%	—	Jun 30, 2026	Northern Funds, not summed
21	VANGUARD PORTFOLIO MANAGEMENT LLC 13F CIK 2100121 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	320,795	0.44%	+320,795	Jun 30, 2026	carried, not yet filed for the newest quarter
22	Zuga Matt Insider CIK 1790214 · Jan 22, 2026 Director, 10% Owner, issuer-wide	304,924	0.42%	-4,160	Jan 22, 2026	Director, 10% Owner, issuer-wide
23	DIMENSIONAL FUND ADVISORS LP 13F CIK 354204 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	291,559	0.40%	+171,803	Jun 30, 2026	carried, not yet filed for the newest quarter
23.1	Dimensional U.S. Small Cap ETF Fund S000070906 · Registered fund · Jul 31, 2026 Dimensional ETF Trust, not summed	100,013	0.14%	+12,232	Jul 31, 2026	Dimensional ETF Trust, not summed
23.2	U.S. MICRO CAP PORTFOLIO Fund S000000948 · Registered fund · Jul 31, 2026 DFA INVESTMENT DIMENSIONS GROUP INC, not summed	38,820	0.05%	+28,065	Jul 31, 2026	DFA INVESTMENT DIMENSIONS GROUP INC, not summed
23.3	Dimensional U.S. Core Equity 2 ETF Fund S000070903 · Registered fund · Jul 31, 2026 Dimensional ETF Trust, not summed	9,637	0.01%	0	Jul 31, 2026	Dimensional ETF Trust, not summed
23.4	Dimensional US Core Equity 1 ETF Fund S000081780 · Registered fund · Jul 31, 2026 Dimensional ETF Trust, not summed	7,149	0.01%	—	Jul 31, 2026	Dimensional ETF Trust, not summed
23.5	U.S. VECTOR EQUITY PORTFOLIO Fund S000000982 · Registered fund · Jul 31, 2026 DFA INVESTMENT DIMENSIONS GROUP INC, not summed	6,420	0.01%	—	Jul 31, 2026	DFA INVESTMENT DIMENSIONS GROUP INC, not summed
24	VANGUARD FIDUCIARY TRUST CO 13F CIK 933478 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	291,240	0.40%	+92,014	Jun 30, 2026	carried, not yet filed for the newest quarter
25	BANK OF AMERICA CORP /DE/ 13F CIK 70858 · Bank · Jun 30, 2026 carried, not yet filed for the newest quarter	274,781	0.38%	-45,435	Jun 30, 2026	carried, not yet filed for the newest quarter
26	BOOTHBAY FUND MANAGEMENT, LLC 13F CIK 1549230 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	273,012	0.38%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
27	ACADIAN ASSET MANAGEMENT LLC 13F CIK 916542 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	270,338	0.37%	+84,488	Jun 30, 2026	carried, not yet filed for the newest quarter
28	Siemers Eric Insider CIK 1866239 · Jan 22, 2026 Chief Medical Officer, issuer-wide	255,371	0.35%	-3,226	Jan 22, 2026	Chief Medical Officer, issuer-wide
29	Doherty James J. Insider CIK 2009718 · Jan 16, 2026 President and CDO, issuer-wide	220,900	0.31%	+166,867	Jan 16, 2026	President and CDO, issuer-wide
30	Stalfort John A III Insider CIK 1709418 · Jun 3, 2026 Director, issuer-wide	220,624	0.31%	+35,500	Jun 3, 2026	Director, issuer-wide
31	Barton Russell Insider CIK 1867418 · Jan 22, 2026 Chief Operating Officer, issuer-wide	205,092	0.28%	-2,777	Jan 22, 2026	Chief Operating Officer, issuer-wide
32	NOMURA HOLDINGS INC 13F CIK 1163653 · Holding company · Jun 30, 2026 carried, not yet filed for the newest quarter	189,712	0.26%	+189,712	Jun 30, 2026	carried, not yet filed for the newest quarter
33	GOLDMAN SACHS GROUP INC 13F CIK 886982 · Holding company · Jun 30, 2026 carried, not yet filed for the newest quarter	183,927	0.25%	-22,756	Jun 30, 2026	carried, not yet filed for the newest quarter
33.1	Goldman Sachs Absolute Return Tracker Fund Fund S000020314 · Registered fund · Aug 31, 2026 GOLDMAN SACHS TRUST, not summed	84,445	0.12%	+40,510	Aug 31, 2026	GOLDMAN SACHS TRUST, not summed
34	BRIDGEWAY CAPITAL MANAGEMENT, LLC 13F CIK 1107261 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	176,171	0.24%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
34.1	Ultra-Small Company Market Fund Fund S000004424 · Registered fund · Jun 30, 2026 Bridgeway Funds, Inc., not summed	87,871	0.12%	0	Jun 30, 2026	Bridgeway Funds, Inc., not summed
34.2	Ultra-Small Company Fund Fund S000004423 · Registered fund · Jun 30, 2026 Bridgeway Funds, Inc., not summed	75,000	0.10%	0	Jun 30, 2026	Bridgeway Funds, Inc., not summed
35	Meisner Derek M Insider CIK 1752461 · Mar 6, 2026 Chief Legal Officer & Corp Sec, issuer-wide	173,999	0.24%	0	Mar 6, 2026	Chief Legal Officer & Corp Sec, issuer-wide
36	MORGAN STANLEY 13F CIK 895421 · Holding company · Jun 30, 2026 carried, not yet filed for the newest quarter	136,763	0.19%	-7,821	Jun 30, 2026	carried, not yet filed for the newest quarter
37	SUSQUEHANNA INTERNATIONAL GROUP, LLP 13F CIK 1446194 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	126,104	0.17%	-475,372	Jun 30, 2026	carried, not yet filed for the newest quarter
38	Bank of New York Mellon Corp 13F CIK 1390777 · Bank · Jun 30, 2026 carried, not yet filed for the newest quarter	124,377	0.17%	+124,377	Jun 30, 2026	carried, not yet filed for the newest quarter
39	CHARLES SCHWAB INVESTMENT MANAGEMENT INC 13F CIK 884546 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	115,099	0.16%	+115,099	Jun 30, 2026	carried, not yet filed for the newest quarter
39.1	Schwab Small-Cap Index Fund Fund S000005912 · Registered fund · Jul 31, 2026 SCHWAB CAPITAL TRUST, not summed	115,088	0.16%	—	Jul 31, 2026	SCHWAB CAPITAL TRUST, not summed
40	PFG Investments, LLC 13F CIK 1973224 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	94,250	0.13%	+13,400	Jun 30, 2026	carried, not yet filed for the newest quarter
41	Schacterle Amy Insider CIK 2042021 · Jan 16, 2026 Chief Regulatory Officer, issuer-wide	92,303	0.13%	+84,600	Jan 16, 2026	Chief Regulatory Officer, issuer-wide
42	CATALYST FINANCIAL PARTNERS LLC 13F CIK 1927537 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	89,699	0.12%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
43	Nuveen, LLC 13F CIK 1871926 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	63,355	0.09%	+63,355	Jun 30, 2026	carried, not yet filed for the newest quarter
43.1	Nuveen Small Cap Blend Index Fund Fund S000005367 · Registered fund · Jul 31, 2026 TIAA-CREF Funds, not summed	63,355	0.09%	—	Jul 31, 2026	TIAA-CREF Funds, not summed
44	MILLENNIUM MANAGEMENT LLC 13F CIK 1273087 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	60,598	0.08%	-599,077	Jun 30, 2026	carried, not yet filed for the newest quarter
45	Squarepoint Ops LLC 13F CIK 1642575 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	52,351	0.07%	+37,336	Jun 30, 2026	carried, not yet filed for the newest quarter
46	CITADEL ADVISORS LLC 13F CIK 1423053 · Registered investment adviser · Jun 30, 2026 carried, not yet filed for the newest quarter	51,049	0.07%	+51,049	Jun 30, 2026	carried, not yet filed for the newest quarter
47	Prospera Financial Services Inc 13F CIK 1541625 · Unknown · Jun 30, 2026 carried, not yet filed for the newest quarter	50,000	0.07%	0	Jun 30, 2026	carried, not yet filed for the newest quarter
48	WELLS FARGO & COMPANY/MN 13F CIK 72971 · Bank · Jun 30, 2026 carried, not yet filed for the newest quarter	49,686	0.07%	+39,578	Jun 30, 2026	carried, not yet filed for the newest quarter
49	EQ/2000 Managed Volatility Portfolio Fund S000025800 · Registered fund · Jun 30, 2026 EQ Advisors Trust, not summed	49,588	0.07%	—	Jun 30, 2026	EQ Advisors Trust, not summed
50	Drapkin Kimberlee C Insider CIK 1340881 · Jun 3, 2026 Director, issuer-wide	48,300	0.07%	+35,500	Jun 3, 2026	Director, issuer-wide

4 more nested rows are not shown here; Every filing lists them all.

Shares are restated onto today's split basis. Change compares each row with the same holder's previous filing in the same source; a dash means there is none to compare. Nested 13D/G, insider and fund rows are not summed, since a 13F report already holds them.

Showing 1–50 of 147 holders

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Key facts CIK 1576885 CUSIP 00509G209 13F (30d) 8 filings 8 filers Visit website Investor relations