Sec Form 4 Filing - Sands Capital Ventures Discovery Fund III, L.P. @ Acumen Pharmaceuticals, Inc. - 2021-07-06

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Sands Capital Ventures Discovery Fund III, L.P. 2. Issuer Name and Ticker or Trading Symbol Acumen Pharmaceuticals, Inc. [ ABOS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 1000 WILSON BLVD., SUITE 3000 3. Date of Earliest Transaction (MM/DD/YY) 07/06/2021 (Street) ARLINGTON, VA22209 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 07/06/2021 C 1,124,729 A 1,124,729 D ( 3 ) ( 5 ) Common Stock 07/06/2021 C 1,842,346 A 2,967,075 D ( 4 ) ( 5 ) Common Stock 07/06/2021 P( 2 ) 450,000 A $ 14.88 3,417,075 D ( 4 ) ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series A-1 Preferred Stock ( 1 ) 07/06/2021 C 1,124,729 ( 1 ) ( 1 ) Common Stock 1,124,729 ( 1 ) 0 D ( 3 ) ( 5 ) Series B Preferred Stock ( 1 ) 07/06/2021 C 1,842,346 ( 1 ) ( 1 ) Common Stock 1,842,346 ( 1 ) 0 D ( 4 ) ( 5 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Sands Capital Ventures Discovery Fund III, L.P. 1000 WILSON BLVD., SUITE 3000 ARLINGTON, VA22209 X Sands Capital Global Venture Fund II, L.P. 1000 WILSON BLVD, SUITE 3000 ARLINGTON, VA22209 X Sands Capital Life Sciences Pulse Fund, LLC 1000 WILSON BLVD, SUITE 3000 ARLINGTON, VA22209 X SANDS FRANK M. 1000 WILSON BLVD, SUITE 3000 ARLINGTON, VA22209 X Signatures /s/ Jonathan Goodman, General Counsel of Sands Capital Ventures Discovery Fund III-GP, LLC, the General Partner of Sands Capital Ventures Discovery Fund III, L.P. 07/08/2021 Signature of Reporting Person Date /s/ Jonathan Goodman, General Counsel of Sands Capital Global Venture Discovery Fund II-GP, LLC, the General Partner of Sands Capital Global Venture Fund II-GP, L.P., the General Partner of Sands Capital Venture Fund II, L.P. 07/08/2021 Signature of Reporting Person Date /s/ Jonathan Goodman, General Counsel of Sands Capital Life Sciences Pulse Fund, LLC 07/08/2021 Signature of Reporting Person Date /s/ Frank M. Sands 07/08/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of Series A-1 Preferred Stock and each share of Series B Preferred Stock automatically converted into one share of Common Stock of the Issuer upon the closing of the Issuer's initial public offering. ( 2 )Represents 225,000 shares of Common Stock acquired by Sands Capital Global Venture Fund II, L.P. ("Sands Venture Fund") and 225,000 shares of Common Stock acquired by ands Capital Life Sciences Pulse Fund ("Sands Pulse Fund") in connection with the closing of the Issuer's initial public offering. ( 3 )Consists of 1,124,719 shares of Common Stock held by Sands Capital Ventures Discovery Fund III, L.P. ("Sands Discovery Fund "). Sands Capital Ventures Discovery Fund III-GP, LLC ("Sands Discovery GP") is the general partner of Sands Discovery Fund. Sands Discovery GP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 4 )Consists of 921,173 shares of Common Stock held by Sands Venture Fund and 921,173 shares of Common Stock held by Sands Pulse Fund. Sands Capital Global Venture Fund II-GP, L.P. ("Sands Venture GP L.P.") is the general partner of Sands Venture Fund and Sands Capital Global Venture Discovery Fund II-GP, LLC ("Sands Venture GP LLC") is the general partner of Sands Venture GP L.P. Sands Venture GP L.P. and Sands Venture GP LLC each disclaims beneficial ownership of such securities except to the extent of its respective pecuniary interest therein. ( 5 )Frank M. Sands holds ultimate voting and investment power over securities held by Sands Discovery Fund, Sands Venture Fund and Sands Pulse Fund. Mr. Sands disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

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