Sec Form 3 Filing - Suhadolnik Kate Eileen @ ESS Tech, Inc. - 2025-08-01

FORM 3 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 Suhadolnik Kate Eileen 2. Issuer Name and Ticker or Trading Symbol ESS Tech, Inc. [ GWH] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Interim CFO (Last) (First) (Middle) C/O ESS TECH, INC., 26440 SW PARKWAY AVE., BLDG. 83 3. Date of Earliest Transaction (MM/DD/YY) 08/01/2025 (Street) WILSONVILLE, OR97070 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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 30,186 D ( 1 ) ( 2 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Suhadolnik Kate Eileen C/O ESS TECH, INC. 26440 SW PARKWAY AVE., BLDG. 83 WILSONVILLE, OR97070 Interim CFO Signatures /s/ Bianca Boschmans, by power of attorney 08/28/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Of the reported shares, 23,805 are represented by restricted stock units, or RSUs, awarded prior to the date on which the reporting person became subject to Section 16. An award representing 394 RSUs was awarded on December 23, 2021. The remaining 48 RSUs vest in two equal quarterly installments beginning on August 20, 2025. An award representing 184 RSUs was awarded on February 8, 2022. The remaining 33 RSUs vest in three equal quarterly installments beginning on August 20, 2025. An award representing 821 RSUs was awarded on November 2, 2022. The remaining 128 RSUs vest in two equal quarterly installments beginning on August 20, 2025. ( 2 )An award representing 5,351 RSUs was awarded on March 13, 2023. The remaining 2,338 RSUs vest in seven equal quarterly installments beginning on August 20, 2025. An award representing 5,867 RSUs was awarded on February 15, 2024. The remaining 4,032 RSUs vest in eleven equal quarterly installments beginning on August 20, 2025. An award representing 18,375 RSUs was awarded on April 13, 2025. The remaining 17,226 RSUs vest in fifteen equal quarterly installments beginning on August 20, 2025.

Remarks: Exhibit 24.1 Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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