ACON / Aclarion, Inc. - Depositi SEC, Relazione annuale, dichiarazione di delega

Aclarion, Inc.

Statistiche di base
LEI 549300KE1U8W5YTMOD89
CIK 1819438
SEC Filings
All companies that sell securities in the United States must register with the Securities and Exchange Commission (SEC) and file reports on a regular basis. These reports include company annual reports (10K, 10Q), news updates (8K), investor presentations (found in 8Ks), insider trades (form 4), ownership reports (13D, and 13G), and reports related to the specific securities sold, such as registration statements and prospectus. This page shows recent SEC filings related to Aclarion, Inc.
SEC Filings (Chronological Order)
Questa pagina fornisce un elenco completo e cronologico dei depositi SEC, esclusi i documenti di proprietà che forniamo altrove.
June 1, 2026 EX-1.01

Conflict Minerals Report of ESS Tech, Inc. For the Year Ended December 31, 2025

EXHIBIT 1.01 Conflict Minerals Report of ESS Tech, Inc. For the Year Ended December 31, 2025 Introduction This Conflict Minerals Report (this “Report”) has been prepared by ESS Tech, Inc. (“ESS,” the “Company,” “we,” “us,” and “our”) in accordance with Rule 13p-1 under the Securities Exchange Act of 1934, as amended, and the requirements of Form SD (collectively, the “Rule”). All terms used but no

June 1, 2026 SD

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.R.S. Employer Identification No.) 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Oregon 97070 (Address of princip

May 29, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 29, 2026 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 29, 2026 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 7, 2026 EX-99.1

ESS Tech, Inc. Announces First Quarter 2026 Financial Results Advancing Commercial Opportunities: Project New Horizon Collaboration with Salt River Project and Google, Large Capacity Energy Storage System for the U.S. Department of the Air and Space

Exhibit 99.1 ESS Tech, Inc. Announces First Quarter 2026 Financial Results Advancing Commercial Opportunities: Project New Horizon Collaboration with Salt River Project and Google, Large Capacity Energy Storage System for the U.S. Department of the Air and Space Force, Strategic Partnership with Alsym, Successful Commissioning of LDES at TID Burbank Water and Power/APPA Efficacy Report Provides Va

May 7, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 7, 2026 ESS TECH, INC. (Exact

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 7, 2026 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.

May 7, 2026 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2026 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 00

April 15, 2026 DEFA14A

Your Vote Counts! ESS TECH, INC. 26440 SW PARKWAY AVE., BLDG. 83 WILSONVILLE, OREGON 97070 ESS TECH, INC. 2026 Annual Meeting Vote by May 28, 2026 11:59 P.M. ET You invested in ESS TECH, INC. and it’s time to vote! You have the right to vote on propo

a2026annualmeetingnotice Your Vote Counts! ESS TECH, INC. 26440 SW PARKWAY AVE., BLDG. 83 WILSONVILLE, OREGON 97070 ESS TECH, INC. 2026 Annual Meeting Vote by May 28, 2026 11:59 P.M. ET You invested in ESS TECH, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the

April 15, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): April 10, 2026 ESS TECH, INC. (Ex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): April 10, 2026 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

April 15, 2026 ARS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2025 OR o TRANSITION REPORT PUR

a2025esstechinc-annualre UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.

April 15, 2026 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) x Definitive Proxy State

March 5, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 5, 2026 ESS TECH, INC. (Exa

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 5, 2026 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (

March 5, 2026 EX-10.24

ESS TECH, INC. AMENDMENT NO. 3 TO PROMISSORY NOTE

ESS TECH, INC. AMENDMENT NO. 3 TO PROMISSORY NOTE This Amendment No. 3 to that certain Promissory Note (this “Amendment”) is effective as of February 27, 2026 by and between ESS Tech, Inc., a Delaware corporation (the “Company”) and YA II PN, LTD., a Cayman Islands exempt limited company, or its registered assigns (the “Holder”). Each such person is referred to herein as a “Party” and, collectivel

March 5, 2026 EX-10.10

ESS TECH, INC. January 1, 2026

ESS TECH, INC. January 1, 2026 Drew Buckley EMPLOYMENT AGREEMENT Dear Drew: This Employment Agreement (the “Agreement”) between you (referred to hereinafter as the “Executive” or “you”) and Ess Tech, Inc. (the “Company”) sets forth the terms and conditions that shall govern the period of Executive’s employment with the Company (referred to hereinafter as “Employment” or the “Employment Period”). 1

March 5, 2026 EX-99.1

ESS Announces Fourth Quarter and Full Year 2025 Financial Results Leadership and Organizational Reset Advancing Next Phase of Growth and Execution Stronger Liquidity Profile Supports Commercial Scale Deployment

Exhibit 99.1 ESS Announces Fourth Quarter and Full Year 2025 Financial Results Leadership and Organizational Reset Advancing Next Phase of Growth and Execution Stronger Liquidity Profile Supports Commercial Scale Deployment WILSONVILLE, OREGON – March 5, 2026 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage (“LDES”)

March 5, 2026 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2025 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-395

March 5, 2026 S-8

As filed with the Securities and Exchange Commission on March 5, 2026

As filed with the Securities and Exchange Commission on March 5, 2026 Registration No.

March 5, 2026 EX-FILING FEES

Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter)

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter) Table 1 - Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered (1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Equity Common Stock, $0.0001 par value

March 5, 2026 EX-4.2

DESCRIPTION OF SECURITIES REGISTERED PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934

Exhibit 4.2 DESCRIPTION OF SECURITIES REGISTERED PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934 The following descriptions of the capital stock of ESS Tech, Inc. (“us,” “our,” “we,” “ESS” or the “Company”) and certain provisions of our certificate of incorporation (as amended by the certificate of amendment to the certificate of incorporation, the “certificate of incorporation”) and

March 5, 2026 EX-21.1

LIST OF SUBSIDIARIES

Exhibit 21.1 LIST OF SUBSIDIARIES None. Pursuant to Item 601(b)(21)(ii) of Regulation S-K, the names of ESS Tech, Inc.’s subsidiary is omitted because it does not constitute a “significant subsidiary” as defined in Regulation S-X.

January 30, 2026 EX-10.1

SECURITIES PURCHASE AGREEMENT

Exhibit 10.1 [***] Portions of this exhibit have been redacted in compliance with Regulation S-K Item 601(a)(6). SECURITIES PURCHASE AGREEMENT This Securities Purchase Agreement (this “Agreement”) is dated as of January 29, 2026, between ESS Tech, Inc., a Delaware corporation (the “Company”), and each purchaser identified on the signature pages hereto (including their respective successors and ass

January 30, 2026 EX-4.1

REGISTERED PRE-FUNDED WARRANT TO PURCHASE COMMON STOCK ESS TECH, INC.

Exhibit 4.1 REGISTERED PRE-FUNDED WARRANT TO PURCHASE COMMON STOCK ESS TECH, INC. Warrant Shares: [●] Initial Exercise Date: January 30, 2026 Issuance Date: January 30, 2026 THIS PRE-FUNDED WARRANT TO PURCHASE COMMON STOCK (the “Warrant”) certifies that, for value received, [●] or its assigns (the “Holder”) is entitled, upon the terms and subject to the limitations on exercise and the conditions h

January 30, 2026 424B5

3,471,428 Shares of Common Stock Pre-Funded Warrants to Purchase up to 5,100,000 Shares of Common Stock 5,100,000 Common Stock Underlying the Pre-Funded Warrants

As filed pursuant to Rule 424(b)(5) Registration No. 333-291506 PROSPECTUS SUPPLEMENT (To Prospectus dated December 11, 2025) 3,471,428 Shares of Common Stock Pre-Funded Warrants to Purchase up to 5,100,000 Shares of Common Stock 5,100,000 Common Stock Underlying the Pre-Funded Warrants We are offering 3,471,428 shares of our common stock, par value $0.0001 per share, and, in lieu of common stock,

January 30, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 29, 2026 ESS TECH, INC. (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 29, 2026 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

January 29, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 23, 2026 ESS TECH, INC. (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 OR 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 23, 2026 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

January 6, 2026 EX-99.1

ESS Tech Appoints Drew Buckley as Chief Executive Officer and Announces New Leadership Changes Recent Head of Capital Markets Strategy and Veteran Technology Investment Executive to Lead Next Phase of Commercial Execution Interim CEO Kelly Goodman Ap

Exhibit 99.1 ESS Tech Appoints Drew Buckley as Chief Executive Officer and Announces New Leadership Changes Recent Head of Capital Markets Strategy and Veteran Technology Investment Executive to Lead Next Phase of Commercial Execution Interim CEO Kelly Goodman Appointed Chief Strategy Officer and General Counsel Interim CFO Kate Suhadolnik Appointed Permanent Chief Financial Officer WILSONVILLE, O

January 6, 2026 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): January 1, 2026 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): January 1, 2026 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

December 11, 2025 424B5

Up to $75,000,000 Common Stock

Filed Pursuant to Rule 424(b)(5) Registration No. 333-291506 PROSPECTUS SUPPLEMENT Up to $75,000,000 Common Stock We have entered into a Sales Agreement, dated November 13, 2025, (the “Sales Agreement”), with Yorkville Securities, LLC (“Yorkville Securities”), BMO Capital Markets Corp. (“BMO”), Canaccord Genuity LLC (“Canaccord”), Needham & Company, LLC (“Needham”) and Stifel, Nicolaus & Company,

December 11, 2025 424B3

Up to 1,181,416 Shares of Common Stock

Filed Pursuant to Rule 424(b)(3) Registration No. 333-291506 PROSPECTUS Up to 1,181,416 Shares of Common Stock This prospectus relates to the resale, from time to time of up to (i) 129,312 shares (the “Bridge Financing Warrant Shares”) of common stock, par value $0.0001 per share (the “Common Stock”), of ESS Tech, Inc., a Delaware corporation (the “Company”), which are issuable upon the exercise o

December 9, 2025 CORRESP

ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83, Wilsonville, Oregon 97070

ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83, Wilsonville, Oregon 97070 December 9, 2025 VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance 100 F Street, N.E. Washington, D.C. 20549 Attention: Kristin Baldwin Re: ESS Tech, Inc. Registration Statement on Form S-3 File No. 333-291506 Acceleration Request Requested Date: December 11, 2025 Requested Time: 4:00 p.m. Eas

December 5, 2025 EX-10.1

ESS TECH, INC. AMENDMENT NO. 2 TO PROMISSORY NOTE

ESS TECH, INC. AMENDMENT NO. 2 TO PROMISSORY NOTE This Amendment No. 2 to that certain Promissory Note (this “Amendment”) is effective as of December 4, 2025 by and between ESS Tech, Inc., a Delaware corporation (the “Company”) and YA II PN, LTD., a Cayman Islands exempt limited company, or its registered assigns (the “Holder”). Each such person is referred to herein as a “Party” and, collectively

December 5, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): December 4, 2025 ESS TECH, INC. (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): December 4, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

November 13, 2025 EX-FILING FEES

Security Type

Calculation of Filing Fee Tables S-3 ESS Tech, Inc. Table 1: Newly Registered and Carry Forward Securities ☐Not Applicable Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Carry Forward Form Type Carry Forward File Number Carry Forward Initial Effe

November 13, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 13, 2025 ESS TECH, INC.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 13, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

November 13, 2025 EX-10.6

ESS TECH, INC. AMENDMENT NO. 1 TO PROMISSORY NOTE

Exhibit 10.6 ESS TECH, INC. AMENDMENT NO. 1 TO PROMISSORY NOTE This Amendment No. 1 to that certain Promissory Note (this “Amendment”) is effective as of October 31, 2025 by and between ESS Tech, Inc., a Delaware corporation (the “Company”) and YA II PN, Ltd., a Cayman Islands exempt limited company, or its registered assigns (the “Holder”). Each such person is referred to herein as a “Party” and,

November 13, 2025 EX-1.1

Sales Agreement dated November 13, 2025 by and among ESS Tech, Inc., Yorkville Securities, LLC, BMO Capital Markets Corp., Canaccord Genuity LLC, Needham & Company, LLC and Stifel, Nicolaus & Company, Incorporated

Exhibit 1.1 ESS TECH, INC. Common Stock (par value $0.0001 per share) Sales Agreement November 13, 2025 Yorkville Securities, LLC 1012 Springfield Avenue Mountainside, NJ 07092 BMO Capital Markets Corp. 151 West 42nd Street, 32nd Floor New York, New York 10036 Canaccord Genuity LLC One Post Office Square, Suite 3000 Boston, MA 02109 Needham & Company, LLC 250 Park Avenue, 10th Floor New York, NY 1

November 13, 2025 EX-10.4

August 12, 2025 Jigish Trivedi

Exhibit 10.4 August 12, 2025 Jigish Trivedi Transmitted by email to [***] Dear Jigish, We are pleased to extend you an offer of employment as Chief Operating Officer, reporting to the Chief Executive Officer with a start date of August 18, 2025. Compensation: •Your annual salary will be $375,000 paid on a semi-monthly basis on the 15th and the 30th. •You will be granted a new hire award of 275,000

November 13, 2025 EX-99.1

ESS Tech, Inc. Announces Third Quarter 2025 Financial Results Announced 50 MWh long-duration storage pilot project with Salt River Project (SRP) Closed $40 million financing with Yorkville Advisors Global and subsequently repaid $15 million of the pr

Exhibit 99.1 ESS Tech, Inc. Announces Third Quarter 2025 Financial Results Announced 50 MWh long-duration storage pilot project with Salt River Project (SRP) Closed $40 million financing with Yorkville Advisors Global and subsequently repaid $15 million of the promissory note; completed the $25 million Standby Equity Purchase Agreement (SEPA) Announced plans to launch a $75 million at-the-market (

November 13, 2025 S-3

As filed with the Securities and Exchange Commission on November 13, 2025

As filed with the Securities and Exchange Commission on November 13, 2025 Registration No.

November 13, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 13, 2025 ESS TECH, INC.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 13, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

November 13, 2025 424B5

Up to $75,000,000 Common Stock

Filed Pursuant to Rule 424(b)(5) Registration No. 333-268138 PROSPECTUS SUPPLEMENT (To Prospectus dated November 17, 2022) Up to $75,000,000 Common Stock We have entered into a Sales Agreement, dated November 13, 2025, (the “Sales Agreement”), with Yorkville Securities, LLC (“Yorkville Securities”), BMO Capital Markets Corp. (“BMO”), Canaccord Genuity LLC (“Canaccord”), Needham & Company, LLC (“Ne

November 13, 2025 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file numbe

November 13, 2025 EX-4.3

ESS TECH, INC. Dated as of , 20 TABLE OF CONTENTS

Exhibit 4.3 ESS TECH, INC. INDENTURE Dated as of , 20 [] Trustee TABLE OF CONTENTS Page ARTICLE I DEFINITIONS AND INCORPORATION BY REFERENCE 1 Section 1.1 Definitions 1 Section 1.2 Other Definitions 4 Section 1.3 Incorporation by Reference of Trust Indenture Act 4 Section 1.4 Rules of Construction 5 ARTICLE II THE SECURITIES 5 Section 2.1 Issuable in Series 5 Section 2.2 Establishment of Terms of

October 22, 2025 424B2

619,694 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 18 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 619,694 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated October 14, 2025, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as suppl

October 17, 2025 424B2

445,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 17 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 445,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated October 14, 2025, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as suppl

October 15, 2025 424B2

1,719,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 16 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 1,719,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated October 14, 2025, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as sup

October 14, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): October 13, 2025 ESS TECH, INC. (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): October 13, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

October 14, 2025 EX-4.1

WARRANT TO PURCHASE SHARES OF COMMON STOCK ESS Tech, Inc. Dated as of October 14, 2025 Void after the date specified in Section 7

Exhibit 4.1 Certain confidential information contained in this exhibit has been omitted because it is both (i) not material; and (ii) the type that the registrants treat as private or confidential. THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE. THESE SECURITIES MAY NOT BE OFFER

October 14, 2025 424B2

Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 15 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) Up to $25,000,000 Common Stock This prospectus supplement amends and supplements the information in the prospectus supplement, dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to

October 14, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): October 14, 2025 ESS TECH, INC. (

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): October 14, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

October 14, 2025 EX-10.1

ESS Tech, Inc. Promissory Note

Exhibit 10.1 Certain confidential information contained in this exhibit has been omitted because it is both (i) not material; and (ii) the type that the registrants treat as private or confidential. THIS HAS NOT BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE. THIS NOTE HAS BEEN SOLD IN RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE SEC

October 14, 2025 EX-99.1

ESS Announces Closing of $40 Million Financing Transaction Transaction Builds on Significant Momentum Following Announcement of 50MWh Energy Base Project in Arizona

Exhibit 99.1 Exhibit 99.1 FOR IMMEDIATE RELEASE ESS Announces Closing of $40 Million Financing Transaction Transaction Builds on Significant Momentum Following Announcement of 50MWh Energy Base Project in Arizona Wilsonville, Ore.– October 14, 2025 - ESS Tech, Inc. (“ESS” or the “Company”) (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage systems for commercial- and util

October 10, 2025 424B2

300,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 14 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 300,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we a

October 9, 2025 424B2

500,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 13 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 500,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we a

October 7, 2025 424B2

630,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 12 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 630,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we a

October 7, 2025 DEFA14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☐ Definitive Proxy State

September 30, 2025 424B2

250,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 11 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 250,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we a

September 25, 2025 144

144

144 0001953607 XXXXXXXX LIVE 0001819438 ESS TECH, INC. 001-39525 26440 SW Parkway Ave Bldg. 83 Wilsonville OR 97070 (855) 423-9920 ANTHONY A RABB Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004 3878 6668.22 14189663 09/25/2025 NYSE Common 05/20/2025 Restricted Stock Issuer N 3878 05/20/2025 Not Applicable N ANTHONY A RABB 264

September 25, 2025 424B2

200,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 10 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 200,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we a

September 22, 2025 ARS

ARS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2024 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39525 ESS Tech, Inc.

September 22, 2025 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) x Definitive Proxy State

September 19, 2025 424B2

200,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 9 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 200,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

September 17, 2025 144

144

144 0001953607 XXXXXXXX LIVE 0001819438 ESS TECH, INC. 001-39525 26440 SW Parkway Ave Bldg. 83 Wilsonville OR 97070 (855) 423-9920 ANTHONY A RABB Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004 3000 4830.30 14189663 09/17/2025 NYSE Common 05/20/2025 Restricted Stock Issuer N 1215 05/20/2025 Not Applicable Common 02/20/2025 Re

September 16, 2025 424B2

97,298 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 8 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 97,298 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we are

September 10, 2025 144

144

144 0001953607 XXXXXXXX LIVE 0001819438 ESS TECH, INC. 001-39525 26440 SW Parkway Ave Bldg. 83 Wilsonville OR 97070 (855) 423-9920 ANTHONY A RABB Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004 4774 6790.54 14189663 09/10/2025 NYSE Common 11/20/2024 Restricted Stock Issuer N 1658 11/20/2024 Not Applicable Common 08/20/2024 Re

September 9, 2025 PRE 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: x Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) o Definitive Proxy State

September 5, 2025 424B2

13,059 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 7 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 13,059 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we are

September 4, 2025 144

144

144 0001953607 XXXXXXXX LIVE 0001819438 ESS TECH, INC. 001-39525 26440 SW Parkway Ave Bldg. 83 Wilsonville OR 97070 (855) 423-9920 ANTHONY A RABB Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004 5001 6375.27 14189663 09/04/2025 NYSE Common 08/20/2024 Restricted Stock Issuer N 1632 08/20/2024 Not Applicable Common 02/20/2025 Re

August 29, 2025 144

144

144 0001953607 XXXXXXXX LIVE 0001819438 ESS TECH, INC. 001-39525 26440 SW Parkway Ave Bldg. 83 Wilsonville OR 97070 (855) 423-9920 ANTHONY A RABB Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004 5062 7538.84 14189663 08/29/2025 NYSE Common 11/20/2023 Restricted Stock Issuer N 1288 11/20/2023 Not Applicable Common 05/20/2023 Re

August 29, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 29, 2025 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 29, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 28, 2025 424B2

34,950 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 6 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 34,950 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we are

August 21, 2025 424B2

110,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 5 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 110,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

August 18, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 12, 2025 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 12, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 15, 2025 424B2

125,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 4 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 125,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

August 14, 2025 EX-10.2

dated July 10, 2025, by and between the

CERTAIN INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY [***], HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE COMPANY TREATS AS PRIVATE OR CONFIDENTIAL.

August 14, 2025 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001

August 14, 2025 EX-99.1

ESS Tech, Inc. Announces Second Quarter 2025 Financial Results Secured up to $31 million in new capital, strengthening balance sheet and extending operational runway Proposal activity exceeding 1.1 GWh following Energy Base launch Strengthened our le

Exhibit 99.1 ESS Tech, Inc. Announces Second Quarter 2025 Financial Results Secured up to $31 million in new capital, strengthening balance sheet and extending operational runway Proposal activity exceeding 1.1 GWh following Energy Base launch Strengthened our leadership team to advance the company vision with the appointment of Jigish Trivedi as COO Operating cash burn reduced by ~80% in June com

August 14, 2025 EX-10.3

Kate Suhadolnik Offer Letter, dated

Exhibit 10.3 Offer Letter 26440 SW Parkway., Wilsonville OR 97070 T: 855-423-9920 We are pleased to offer you, Kate Suhadolnik the position of SEC Reporting Manager, with ESS Tech., Inc. (the “Company”) effective upon your signing of this letter, and the Employee Proprietary Information and Inventions Assignment Agreement (EPIIAA) explained below. •Your full-time, [X] exempt employment with the Co

August 14, 2025 EX-4.8

orm of Warrant to P

Exhibit 4.8 THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE. THESE SECURITIES MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED EXCEPT AS PERMITTED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAWS IN ACCORDANCE WITH APPLICABLE REGISTRATION REQUIREMENTS

August 14, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 14, 2025 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 14, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 7, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 1, 2025 ESS TECH, INC. (Ex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 1, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

July 28, 2025 424B2

500,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 3 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 500,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

July 22, 2025 424B2

500,000 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 2 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 500,000 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

July 15, 2025 424B2

214,633 Shares of Common Stock

Filed Pursuant to Rule 424(b)(2) Registration No. 333-268138 Prospectus Supplement No. 1 (to Prospectus dated November 17, 2022 and Prospectus Supplement dated July 11, 2025) 214,633 Shares of Common Stock Pursuant to this prospectus supplement, the prospectus supplement dated July 11, 2025 and the base prospectus dated November 17, 2022 (as supplemented from time to time, the “Prospectus”), we ar

July 11, 2025 424B3

The date of this Supplement No. 1 is July 11, 2025.

Filed Pursuant to Rule 424(b)(3) Registration No. 333-268138 SUPPLEMENT NO. 1 TO PROSPECTUS SUPPLEMENT DATED MARCH 31, 2025 (To Prospectus dated November 17, 2022) This Supplement No. 1 to Prospectus Supplement (this “Supplement No. 1”) amends and supplements the information in the prospectus, dated November 17, 2022, (the “Prospectus”), and the prospectus supplement, dated March 31, 2025 (the “AT

July 11, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 9, 2025 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): July 9, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

July 11, 2025 EX-10.1

Standby Equity Purchase Agreement, dated July 9, 2025, by and between ESS Tech, Inc. and YA II PN, LTD.

Exhibit 10.1 Execution Version STANDBY EQUITY PURCHASE AGREEMENT THIS STANDBY EQUITY PURCHASE AGREEMENT (this “Agreement”) dated as of July 9, 2025, is made by and between YA II PN, LTD., a Cayman Islands exempt limited company (the “Investor”), and ESS TECH, INC., a company incorporated under the laws of the State of Delaware (the “Company”). The Investor and the Company may be referred to herein

July 11, 2025 EX-99.1

ESS Announces $31M Insider-Led Funding Package to Continue Execution of Strategic Shift and Secures First Energy Base Order

Exhibit 99.1 Exhibit 99.1 FOR IMMEDIATE RELEASE ESS Announces $31M Insider-Led Funding Package to Continue Execution of Strategic Shift and Secures First Energy Base Order Wilsonville, Ore.– July 11, 2025 - ESS Tech, Inc. (“ESS” or the “Company”) (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage (LDES) systems for commercial- and utility-scale applications, today announc

July 11, 2025 424B2

Up to $6,643,395 Common Stock

As filed pursuant to Rule 424(b)(2) Registration No. 333-268138 PROSPECTUS SUPPLEMENT (To Prospectus dated November 17, 2022) Up to $6,643,395 Common Stock ESS Tech, Inc. (the “Company”) entered into a Standby Equity Purchase Agreement with YA II PN, LTD., a Cayman Islands exempt limited company (“Yorkville”), on July 9, 2025 (the “SEPA”). The Company shall have the right, but not the obligation,

June 4, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 3, 2025 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): June 3, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 30, 2025 EX-1.01

Conflict Minerals Report of ESS Tech, Inc. for the year ended December 31, 202

EXHIBIT 1.01 Conflict Minerals Report of ESS Tech, Inc. For the Year Ended December 31, 2024 Introduction This Conflict Minerals Report (this "Report) has been prepared by ESS Tech, Inc. (“ESS,” the “Company,” “we,” “us,” and “our”) in accordance with Rule 13p-1 under the Securities Exchange Act of 1934, as amended, and the requirements of Form SD (collectively, the “Rule”). All terms used but not

May 30, 2025 SD

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.R.S. Employer Identification No.) 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Oregon 97070 (Address of princip

May 28, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 27, 2025 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): May 27, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 15, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 15, 2025 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 15, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 15, 2025 EX-99.1

ESS Tech, Inc. Announces First Quarter 2025 Financial Results In Contracting for 50 MWh Energy Base Award with Arizona based Utility Proposal Activity up to ~1.2 GWh and Growing following Energy Base Product Launch Energy Warehouse Startup Completed

Exhibit 99.1 ESS Tech, Inc. Announces First Quarter 2025 Financial Results In Contracting for 50 MWh Energy Base Award with Arizona based Utility Proposal Activity up to ~1.2 GWh and Growing following Energy Base Product Launch Energy Warehouse Startup Completed in the Second Quarter for California Irrigation District systems ESS’ Made in the USA batteries Well Positioned to Navigate Tariff Volati

May 15, 2025 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 00

March 31, 2025 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2024 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-395

March 31, 2025 EX-1.1

Sales Agreement, dated March 31, 2025, by and between ESS Tech, Inc. and Robert W. Baird & Co. Incorporated

Exhibit 1.1 CERTAIN OF THE EXHIBITS AND SCHEDULES TO THIS EXHIBIT HAVE BEEN OMITTED IN ACCORDANCE WITH REGULATION S-K ITEM 601(A)(5). ESS TECH, INC. Common Stock ($0.0001 par value per share) Sales Agreement March 31, 2025 Robert W. Baird & Co. Incorporated 777 East Wisconsin Avenue Milwaukee, Wisconsin 53202 Ladies and Gentlemen: ESS Tech, Inc., a Delaware Corporation (the “Company”), confirms it

March 31, 2025 EX-19.1

ESS Tech, Inc. Insider Trading Policy

ESS TECH, INC. INSIDER TRADING POLICY (As amended on August 8, 2024) A.POLICY OVERVIEW ESS Tech, Inc. (together with any subsidiaries, collectively the “Company”) has adopted this Insider Trading Policy (the “Policy”) to help you comply with the federal and state securities laws and regulations that govern trading in securities and to help the Company minimize its own legal and reputational risk.

March 31, 2025 EX-4.2

Exhibit 4.2

Exhibit 4.2 DESCRIPTION OF CAPITAL STOCK The following descriptions of the capital stock of ESS Tech, Inc. (“us,” “our,” “we,” “ESS” or the “Company”) and certain provisions of our certificate of incorporation (as amended, the “certificate of incorporation”) and amended and restated bylaws are summaries and are qualified by reference to the certificate of incorporation and the amended and restated

March 31, 2025 EX-99.1

ESS Tech, Inc. Announces Fourth Quarter and Full Year 2024 Financial Results Completed Commissioning and Grid Interconnection of First Two Energy Centers Delivered Eight Energy Center Systems to Florida Utility Achieved Breakeven Profitability on Ene

Exhibit 99.1 ESS Tech, Inc. Announces Fourth Quarter and Full Year 2024 Financial Results Completed Commissioning and Grid Interconnection of First Two Energy Centers Delivered Eight Energy Center Systems to Florida Utility Achieved Breakeven Profitability on Energy Center Design at the end of Q4, Almost a Year Ahead of Schedule Announced Energy Base, a New Modular, Non-Containerized Gigawatt-Hour

March 31, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 31, 2025 ESS TECH, INC. (Ex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 31, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

March 31, 2025 EX-10.8

Amended and Restated Outside Director Compensation Policy

Exhibit 10.8 ESS TECH, INC. OUTSIDE DIRECTOR COMPENSATION POLICY ESS Tech, Inc. (the “Company”) believes that providing cash and equity compensation to its members of the Board of Directors (the “Board,” and members of the Board, the “Directors”) represents an effective tool to attract, retain and reward Directors who are not employees of the Company (the “Outside Directors”). This Outside Directo

March 31, 2025 EX-21.1

List of Subsidiaries

Exhibit 21.1 LIST OF SUBSIDIARIES None.

March 31, 2025 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 31, 2025 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

March 31, 2025 EX-97.1

Compensation Recovery Policy

ESS TECH, INC. COMPENSATION RECOVERY POLICY As adopted on November 1, 2023 ESS Tech, Inc. (the “Company”) is committed to strong corporate governance. As part of this commitment, the Company’s Board of Directors (the “Board”) has adopted this clawback policy called the Compensation Recovery Policy (the “Policy”). This Policy is intended to further the Company’s pay-for-performance philosophy and t

March 31, 2025 EX-FILING FEES

Calculation of Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter) Table 1 - Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered (1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Equity Common Stock, $0.0001 par value

March 31, 2025 424B5

Up to $13,504,438 Common Stock

Filed Pursuant to Rule 424(b)(5) Registration No. 333-268138 PROSPECTUS SUPPLEMENT (To Prospectus dated November 17, 2022) Up to $13,504,438 Common Stock We have entered into a Sales Agreement, dated March 31, 2025, (the “Sales Agreement”), with Robert W. Baird & Co. Incorporated relating to shares of our common stock, $0.0001 par value per share, offered by this prospectus supplement and the acco

March 31, 2025 EX-10.11

, 2025, by and between ESS Tech

Exhibit 10.11 SEPARATION AGREEMENT AND RELEASE This Separation Agreement and Release (“Agreement”) is made by and between Eric Dresselhuys (“Executive”) and ESS Tech, Inc. (the “Company”) (jointly referred to as the “Parties” or individually referred to as a “Party”). RECITALS WHEREAS, Executive was employed by the Company at-will; WHEREAS, Executive signed an April 1, 2021 Employment Agreement wi

March 31, 2025 EX-10.16

Kelly Goodman Offer Letter

Exhibit 10.16 February 14, 2022 Dear Kelly, As discussed, we are extending to you an offer of employment as Vice President of Legal reporting Eric Dresselhuys with a tentative start date of March 14, 2022. Compensation: •Your annual salary will be $255,000, paid out on a bi-monthly basis of $10,625. •As a part of accepting this offer, you will be granted restricted stock units valued at $600,000.

March 31, 2025 EX-10.15

Credit Agreement, dated November 1, 2024, by and between ESS Tech, Inc. and Export-Import Bank of the United States

Exhibit 10.14 CERTAIN IDENTIFIED INFORMATION HAS BEEN EXCLUDED FROM THE EXHIBIT BECAUSE IT IS BOTH NOT MATERIAL AND IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. Execution Version CREDIT AGREEMENT dated as of November 1, 2024 among ESS TECH, INC. as Borrower and EXPORT-IMPORT BANK OF THE UNITED STATES EXIM Bank Transaction No. AP089503XX EXIM Bank Transaction No. AP089503XX Te

March 31, 2025 S-8

As filed with the Securities and Exchange Commission on March 31, 2025

As filed with the Securities and Exchange Commission on March 31, 2025 Registration No.

March 28, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 24, 2025 ESS TECH, INC. (Ex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): March 24, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

March 28, 2025 EX-99.1

-2-

ESS Tech, Inc. Receives NYSE Notification March 28, 2025 WILSONVILLE, Ore.-(BUSINESS WIRE)- ESS Tech, Inc. (ESS) (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage (LDES) systems for utility- and commercial- scale applications, today announced that on March 24, 2025, it received a notice (the “Notice”) from the New York Stock Exchange (the “NYSE”) that ESS is not in compl

February 14, 2025 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2025 ESS TECH, INC.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): February 13, 2025 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

February 14, 2025 EX-99.1

ESS Announces Actions to Position the Company for the Future Kelly Goodman appointed interim CEO and Board Engages Financial Advisors

Exhibit 99.1 ESS Announces Actions to Position the Company for the Future Kelly Goodman appointed interim CEO and Board Engages Financial Advisors Wilsonville, Ore.– February 13, 2025 - ESS Tech, Inc. (ESS) (NYSE:GWH), a leading manufacturer of iron flow long-duration energy storage (LDES) systems for utility- and commercial- scale applications, today announced changes with the intent to take the

November 14, 2024 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file numbe

November 13, 2024 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 13, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

November 13, 2024 EX-99.1

ESS Tech, Inc. Announces Third Quarter 2024 Financial Results Installed and Commissioned Second Energy Center

Exhibit 99.1 ESS Tech, Inc. Announces Third Quarter 2024 Financial Results Installed and Commissioned Second Energy Center WILSONVILLE, Ore. – November 13, 2024 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE: GWH), a leading manufacturer of long-duration energy storage systems (LDES) for commercial and utility-scale applications, today announced financial results for its third quarte

November 5, 2024 8-K

Entry into a Material Definitive Agreement, Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): November 1, 2024 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

November 1, 2024 SC 13D/A

ACON / Aclarion, Inc. / Evans Craig E - SC 13D/A Activist Investment

SC 13D/A 1 ess-schedule13daevanssong.htm SC 13D/A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D UNDER THE SECURITIES EXCHANGE ACT OF 1934 (Amendment No. 1)* ESS Tech, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 26916J106 (CUSIP Number) Craig Evans Julia Song ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83 Wils

August 26, 2024 8-K/A

Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K/A (Amendment No. 1) CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 23, 2024 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Com

August 23, 2024 8-K

Regulation FD Disclosure, Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Material Modification to Rights of Security Holders, Financial Statements and Exhibits, Other Events, Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): August 23, 2024 ESS TECH, INC. (Exact name of registrant as specified in charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 23, 2024 EX-99.1

ESS Tech, Inc. Announces Reverse Stock Split August 23, 2024

Exhibit 99.1 ESS Tech, Inc. Announces Reverse Stock Split August 23, 2024 WILSONVILLE, Ore. - ESS Tech, Inc. (“ESS,” “ESS Inc.”) (NYSE:GWH), a leading manufacturer of long-duration energy storage systems (LDES) for commercial and utility-scale applications, today announced that it will effect a 1-for-15 reverse stock split of ESS’ issued and outstanding common stock, par value $0.0001 per share. T

August 23, 2024 EX-3.1

Certificate of Amendment to the Certificate of Incorporation

Exhibit 3.1 CERTIFICATE OF AMENDMENT OF CERTIFICATE OF INCORPORATION OF ESS TECH, INC. ESS Tech, Inc., a Delaware corporation (the “Company”), hereby certifies as follows: 1. The name of the Company is ESS Tech, Inc. and the Company was first formed on July 21, 2020, under the laws of the Cayman Islands, under the name “ACON S2 Acquisition Corp.” 2. The Company filed a certificate of domestication

August 14, 2024 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 14, 2024 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 14, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 14, 2024 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001

August 14, 2024 EX-99.1

ESS Tech, Inc. Announces Second Quarter 2024 Financial Results Finalizing Funding Agreement for up to $50 Million with Export-Import Bank of the United States Began Production of Second Energy Center for Portland General Electric Energy Warehouse Bec

Exhibit 99.1 ESS Tech, Inc. Announces Second Quarter 2024 Financial Results Finalizing Funding Agreement for up to $50 Million with Export-Import Bank of the United States Began Production of Second Energy Center for Portland General Electric Energy Warehouse Becomes First Operational Long-Duration Energy Storage at an Airport Exited Q2 with Cash and Short-Term Investments over $74 Million; Expect

August 8, 2024 DEFR14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant ☒ Filed by a party other than the Registrant ☐ Check the appropriate box: ☐ Preliminary Proxy Statement ☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) ☒ Definitive Proxy State

July 29, 2024 PRE 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant Filed by a party other than the Registrant Check the appropriate box: Preliminary Proxy Statement Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) Definitive Proxy Statement Defin

July 26, 2024 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant Filed by a party other than the Registrant Check the appropriate box: Preliminary Proxy Statement Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) Definitive Proxy Statement Defin

May 24, 2024 SD

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.R.S. Employer Identification No.) 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Oregon 97070 (Address of princip

May 24, 2024 EX-1.01

Conflict Minerals Report of ESS Tech, Inc. for the year ended December 31, 2023, as required by Items 1.01 and 1.02 of this Form SD.

EXHIBIT 1.01 Conflict Minerals Report of ESS Tech, Inc. For the Year Ended December 31, 2023 Introduction ESS Tech, Inc. (“ESS,” the “Company,” “we,” “us,” and “our”), has prepared this Conflict Minerals Report (this “Report”) pursuant to Rule 13p-1 under the Securities Exchange Act of 1934, as amended, and the requirements of Form SD (collectively, the “Rule”). All terms used but not defined in t

May 21, 2024 8-K

Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 21, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 8, 2024 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 00

May 7, 2024 EX-99.1

ESS Tech, Inc. Announces First Quarter 2024 Financial Results Q1 Revenue of $2.7 Million Partnered with Sapele Power to Supply LDES in Africa Completed Testing of First Energy Center for Portland General Electric Ordered Second Power Module Automatio

Exhibit 99.1 ESS Tech, Inc. Announces First Quarter 2024 Financial Results Q1 Revenue of $2.7 Million Partnered with Sapele Power to Supply LDES in Africa Completed Testing of First Energy Center for Portland General Electric Ordered Second Power Module Automation Line with 40% Greater Production Capacity Exited Q1 with Cash and Short-Term Investments over $89 million; Expected to Carry ESS Well I

May 7, 2024 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 7, 2024 ESS TECH, INC. (Exact

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 7, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.

April 5, 2024 DEFA14A

Your Vote Counts! *Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number For complete information and to vote, visit www.ProxyVote.co

Your Vote Counts! *Please check the meeting materials for any special requirements for meeting attendance.

April 5, 2024 ARS

ARS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2023 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39525 ESS Tech, Inc.

April 5, 2024 DEFA14A

DEFA14A

Your Vote Counts! *Please check the meeting materials for any special requirements for meeting attendance.

April 5, 2024 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) x Definitive Proxy State

March 14, 2024 EX-10.17

Executive Incentive Compensation Plan

ESS TECH, INC. EXECUTIVE INCENTIVE COMPENSATION PLAN 1.Purposes of the Plan. The Plan is intended to increase stockholder value and the success of the Company by motivating Employees to (i) perform to the best of their abilities and (ii) achieve the Company’s objectives. 2.Definitions. (a)“Actual Award” means as to any Performance Period, the actual award (if any) payable to a Participant for the

March 14, 2024 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2023 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-395

March 14, 2024 EX-10.11

Amended and Restated Outside Director Compensation Policy

ESS TECH, INC. OUTSIDE DIRECTOR COMPENSATION POLICY ESS Tech, Inc. (the “Company”) believes that providing cash and equity compensation to its members of the Board of Directors (the “Board,” and members of the Board, the “Directors”) represents an effective tool to attract, retain and reward Directors who are not employees of the Company (the “Outside Directors”). This Outside Director Compensatio

March 14, 2024 EX-4.2

Description of securities

Exhibit 4.2 DESCRIPTION OF SECURITIES REGISTERED PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934 The following descriptions of the capital stock of ESS Tech, Inc. (“us,” “our,” “we,” “ESS” or the “Company”) and certain provisions of our certificate of incorporation (as amended by the certificate of amendment to the certificate of incorporation, the “certificate of incorporation”) and

March 13, 2024 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 13, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

March 13, 2024 EX-99.1

ESS Tech, Inc. Announces Fourth Quarter and Full Year 2023 Financial Results Lowered Q4 Adjusted EBITDA loss by More Than 50% year over year Exited 2023 with Cash and Short-Term Investments over $100 million; Expected to Carry ESS Well Into H1’25 Del

Exhibit 99.1 ESS Tech, Inc. Announces Fourth Quarter and Full Year 2023 Financial Results Lowered Q4 Adjusted EBITDA loss by More Than 50% year over year Exited 2023 with Cash and Short-Term Investments over $100 million; Expected to Carry ESS Well Into H1’25 Delivered First Energy Warehouses to Honeywell Energy Warehouse manufacturing cost lowered by 60% in 2023 Target 40% 2024 EW Cost Reduction

March 8, 2024 EX-99.1

ESS Tech, Inc. Receives Continued Listing Standard Notice From NYSE

ESS Tech, Inc. Receives Continued Listing Standard Notice From NYSE WILSONVILLE, OREGON – March 8, 2024 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE:GWH), a leading manufacturer of long-duration energy storage systems (LDES) for commercial and utility-scale applications, today announced that on March 6, 2024, it received notice (the “Notice”) from the New York Stock Exchange (the “

March 8, 2024 8-K

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing, Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 6, 2024 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (

February 14, 2024 EX-99.1

JOINT FILING AGREEMENT

EX-99.1 2 tm246081d1ex99-1.htm EXHIBIT 99.1 EXHIBIT 99.1 CUSIP No. 26916J106 JOINT FILING AGREEMENT THIS JOINT FILING AGREEMENT is entered into as of February 14, 2024, by and among the parties signatories hereto. The undersigned hereby agree that the Statement on Schedule 13D with respect to the shares of Common Stock of ESS Tech, Inc. is, and any amendment thereafter signed by each of the unders

February 14, 2024 SC 13G/A

STWO / ACON S2 Acquisition Corp - Class A / Cycle Capital Fund III, L.P. - SC 13G/A Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G/A Under the Securities Exchange Act of 1934 (Amendment No. 1)* ESS Tech, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 26916J106 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule

February 9, 2024 EX-FILING FEES

Calculation of Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter) Table 1 - Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered (1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Equity Common Stock, $0.0001 par value

February 9, 2024 S-8

As filed with the Securities and Exchange Commission on February 9, 2024

As filed with the Securities and Exchange Commission on February 9, 2024 Registration No.

January 31, 2024 SC 13G/A

STWO / ACON S2 Acquisition Corp - Class A / Pangaea Ventures Fund III, LP Passive Investment

SC 13G/A 1 formsc13ga.htm UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 3)* ESS Tech, Inc. (Name of Issuer) Common stock, par value $0.0001 per share (Title of Class of Securities) 26916J106 (CUSIP Number) December 31, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate bo

December 15, 2023 424B3

Up to 16,491,754 Shares of Common Stock Warrants to Purchase up to 17,677,348 Shares of Common Stock Up to 17,677,348 Shares of Common Stock Underlying Warrants

Filed Pursuant to Rule 424(b)(3) Registration No. 333-275552 PROSPECTUS Up to 16,491,754 Shares of Common Stock Warrants to Purchase up to 17,677,348 Shares of Common Stock Up to 17,677,348 Shares of Common Stock Underlying Warrants This prospectus relates to the resale from time to time by the selling securityholders described in this prospectus or their permitted transferees (the “Selling Securi

December 12, 2023 CORRESP

ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Or, 97070

ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Or, 97070 December 12, 2023 VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance 100 F Street, N.E. Washington, D.C. 20549 Attention: Erin Donahue Jay Ingram Re: ESS Tech, Inc. Registration Statement on Form S-3 File No. 333-275552 Acceleration Request Requested Date: December 14, 2023 Requested Time: 4:30 p.m

December 7, 2023 CORRESP

December 7, 2023

Wilson Sonsini Goodrich & Rosati Professional Corporation 650 Page Mill Road Palo Alto, California 94304-1050 o: 650.

December 7, 2023 S-3/A

As filed with the Securities and Exchange Commission on December 7, 2023

As filed with the Securities and Exchange Commission on December 7, 2023 Registration No.

November 20, 2023 LETTER

LETTER

United States securities and exchange commission logo November 20, 2023 Eric Dresselhuys Chief Executive Officer ESS Tech, Inc.

November 14, 2023 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file numbe

November 14, 2023 EX-4.6

Performance Warrant, dated September 21, 2023

Execution Version THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE.

November 14, 2023 EX-4.4

Investment Warrant, dated September 21, 2023

Execution Version THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE.

November 14, 2023 S-3

As filed with the Securities and Exchange Commission on November 14, 2023

As filed with the Securities and Exchange Commission on November 14, 2023 Registration No.

November 14, 2023 EX-4.7

Registration Rights Agreement, dated September 21, 2023, by and between the Company and Honeywell ACS Ventures LLC

Execution Version REGISTRATION RIGHTS AGREEMENT This Registration Rights Agreement (this “Agreement”) is made and entered into as of September 21, 2023 (the “Effective Date”) by and between ESS Tech, Inc.

November 14, 2023 EX-10.1

Common Stock and Warrant Purchase Agreement, dated September 21, 2023, by and between the Company and Honeywell ACS Ventures LLC

Execution Version COMMON STOCK AND WARRANT PURCHASE AGREEMENT This Common Stock and Warrant Purchase Agreement (this “Agreement”) is dated as of September 21, 2023, by and between ESS Tech, Inc.

November 14, 2023 EX-4.5

IP Warrant, dated September 21, 2023

Execution Version THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR UNDER THE SECURITIES LAWS OF ANY STATE.

November 14, 2023 EX-FILING FEES

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Table Form S-3 (Form Type) ESS TECH, INC. (Exact Name of Registrant as Specified in its Charter) Table 1 - Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered(1) Proposed Maximum Offering Price Per Security Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Fees to be Paid Equity Common Stock,

November 7, 2023 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 7, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

November 7, 2023 EX-99.1

ESS Tech, Inc. Announces Third Quarter 2023 Financial Results Announced Strategic Partnership with Honeywell

Exhibit 99.1 ESS Tech, Inc. Announces Third Quarter 2023 Financial Results Announced Strategic Partnership with Honeywell WILSONVILLE, Ore. – November 7, 2023 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE: GWH), a leading manufacturer of long-duration energy storage systems for commercial and utility-scale applications, today announced financial results for its third quarter ended S

September 25, 2023 8-K

Regulation FD Disclosure, Entry into a Material Definitive Agreement, Unregistered Sales of Equity Securities, Financial Statements and Exhibits, Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): September 25, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numb

September 25, 2023 SC 13G

STWO / ACON S2 Acquisition Corp - Class A / HONEYWELL INTERNATIONAL INC - SC 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 ESS Tech, Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 26916J106 (CUSIP Number) September 21, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: ¨ Rule

September 25, 2023 EX-99.1

HONEYWELL AND ESS TECH, INC. COLLABORATE TO ACCELERATE COMMERCIAL DEPLOYMENT OF IRON FLOW BATTERY ENERGY STORAGE SYSTEMS

Media Contacts: Honeywell: Mike Hockey +1 (832) 285-4933 [email protected] ESS: Morgan Pitts +1 (503) 568-0755 [email protected] HONEYWELL AND ESS TECH, INC. COLLABORATE TO ACCELERATE COMMERCIAL DEPLOYMENT OF IRON FLOW BATTERY ENERGY STORAGE SYSTEMS CHARLOTTE, NC and WILSONVILLE, OR – September 25, 2023 - Honeywell (Nasdaq: HON) today announced a strategic collaboration with ESS Tech

August 29, 2023 EX-99.1

Harry Quarls Joins ESS Board of Directors as Chairman Energy industry veteran to further accelerate growth

Harry Quarls Joins ESS Board of Directors as Chairman Energy industry veteran to further accelerate growth WILSONVILLE, Ore.

August 29, 2023 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 28, 2023 ESS TECH, INC. (E

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 28, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 9, 2023 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001

August 8, 2023 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 8, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 8, 2023 EX-99.1

ESS Tech, Inc. Announces Second Quarter 2023 Financial Results Record Revenue of $2.8 Million Delivered Energy Warehouses™ to Four New Customers Announces Partnership with LEAG

Exhibit 99.1 ESS Tech, Inc. Announces Second Quarter 2023 Financial Results Record Revenue of $2.8 Million Delivered Energy Warehouses™ to Four New Customers Announces Partnership with LEAG WILSONVILLE, Ore. – August 8, 2023 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE: GWH), a leading manufacturer of long-duration energy storage systems for commercial and utility-scale application

July 13, 2023 SC 13D

STWO / ACON S2 Acquisition Corp - Class A / Evans Craig E - SC 13D Activist Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13D UNDER THE SECURITIES EXCHANGE ACT OF 1934 (Amendment No. )* ESS Tech, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 26916J106 (CUSIP Number) Craig Evans Julia Song ESS Tech, Inc. 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Oregon 97070 (855) 423-9920 (Name, Address

July 13, 2023 EX-3

Joint Filing Agreement, dated July 13, 2023, by and between Craig Evans and Dr. Julia Song.

Exhibit 3 JOINT FILING AGREEMENT In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the common stock, par value $0.

May 24, 2023 EX-1.01

Conflict Minerals Report of ESS Tech, Inc. for the year ended December 31, 2022, as required by Items 1.01 and 1.02 of this Form SD.

EXHIBIT 1.01 Conflict Minerals Report of ESS Tech, Inc. For the Year Ended December 31, 2022 Introduction ESS Tech, Inc. (“ESS,” the “Company,” “we,” “us,” and “our”), has prepared this Conflict Minerals Report (this “Report”) pursuant to Rule 13p-1 under the Securities Exchange Act of 1934, as amended, and the requirements of Form SD (collectively, the “Rule”). All terms used but not defined in t

May 24, 2023 SD

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter)

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM SD SPECIALIZED DISCLOSURE REPORT ESS Tech, Inc. (Exact name of the registrant as specified in its charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.R.S. Employer Identification No.) 26440 SW Parkway Ave., Bldg. 83 Wilsonville, Oregon 97070 (Address of princip

May 22, 2023 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 22, 2023 ESS TECH, INC. (Exac

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 22, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 22, 2023 EX-3.1

Certificate of Amendment to the Certificate of Incorporation

Exhibit 3.1 CERTIFICATE OF AMENDMENT TO THE CERTIFICATE OF INCORPORATION OF ESS TECH, INC. (Pursuant to Section 242 of the General Corporation Law of the State of Delaware) ESS Tech, Inc., a corporation organized and existing under the laws of the State of Delaware, DOES HEREBY CERTIFY: FIRST: That the name of the corporation is ESS Tech, Inc. (the “Corporation”) and that the Corporation was first

May 10, 2023 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 00

May 9, 2023 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 9, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.

May 9, 2023 EX-99.1

ESS Tech, Inc. Announces First Quarter 2023 Financial Results Announces Partnership with Coldwell Solar

Exhibit 99.1 ESS Tech, Inc. Announces First Quarter 2023 Financial Results Announces Partnership with Coldwell Solar WILSONVILLE, Ore. – May 9, 2023 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE: GWH), a leading manufacturer of long-duration energy storage systems for commercial and utility-scale applications, today announced financial results for its first quarter of 2023 ended Mar

May 3, 2023 DEFA14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) o Definitive Proxy State

May 3, 2023 DEFA14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) o Definitive Proxy State

May 3, 2023 8-K

Financial Statements and Exhibits, Changes in Registrant's Certifying Accountant

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 3, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I.

May 3, 2023 EX-16.1

Letter from Ernst & Young LLP

May 3, 2023 Securities and Exchange Commission 100 F Street, N.E. Washington, DC 20549 Ladies and Gentlemen: Refer to our letter issued with Item 4.01 of Form 8-K dated 14 April 2023 of ESS Tech, Inc. /s/ Ernst & Young LLP

April 14, 2023 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): April 10, 2023 ESS TECH, INC. (Ex

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): April 10, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

April 14, 2023 EX-16.1

Letter from Ernst & Young LLP

April 14, 2023 Securities and Exchange Commission 100 F Street, N.E. Washington, DC 20549 Ladies and Gentlemen: We have read Item 4.01 of Form 8-K dated 14 April 2023, of ESS Tech, Inc. and are in agreement with the statements contained in the first, second, third, and fourth paragraph on page two therein. Regarding the registrant’s statement concerning the lack of internal control to prepare fina

April 7, 2023 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) x Definitive Proxy State

April 7, 2023 DEFA14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) o Definitive Proxy State

April 7, 2023 ARS

ARS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2022 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-39525 ESS Tech, Inc.

March 29, 2023 SC 13G

STWO / ACON S2 Acquisition Corp - Class A / Cycle Capital Fund III, L.P. - SC 13G Passive Investment

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. )* ESS Tech, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 26916J106 (CUSIP Number) March 29, 2023 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursua

March 29, 2023 EX-99.1

JOINT FILING AGREEMENT

EXHIBIT 99.1 CUSIP No. 26916J106 JOINT FILING AGREEMENT THIS JOINT FILING AGREEMENT is entered into as of March 29, 2023, by and among the parties signatories hereto. The undersigned hereby agree that the Statement on Schedule 13D with respect to the shares of Common Stock of ESS Tech, Inc. is, and any amendment thereafter signed by each of the undersigned shall be, filed on behalf of each undersi

March 23, 2023 PRE 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

PRE 14A 1 a2022esstechinc-preliminar.htm PRE 14A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: x Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permit

March 2, 2023 EX-4.2

Description of securities

Exhibit 4.2 DESCRIPTION OF SECURITIES REGISTERED PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934 The following descriptions of the capital stock of ESS Tech, Inc. (“us,” “our,” “we,” “ESS” or the “Company”) and certain provisions of our amended and restated certificate of incorporation and amended and restated bylaws are summaries and are qualified by reference to the amended and res

March 2, 2023 EX-10.10

2021 Employee Stock Purchase Plan

ESS TECH, INC. 2021 EMPLOYEE STOCK PURCHASE PLAN 1.Purpose. The purpose of the Plan is to provide employees of the Company and its Designated Companies with an opportunity to purchase Shares through accumulated Contributions. The Company intends for the Plan to have two components: a component that is intended to qualify as an “employee stock purchase plan” under Section 423 of the Code (the “423

March 2, 2023 EX-FILING FEES

Calculation of Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter) Table 1 – Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered(1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Equity Common Stock, $0.0001 par value

March 2, 2023 S-8

As filed with the Securities and Exchange Commission on March 2, 2023

As filed with the Securities and Exchange Commission on March 2, 2023 Registration No.

March 2, 2023 EX-10.14

Employment Agreement, dated November 1, 2022, by and between ESS Tech, Inc. and Anthony Rabb

26440 SW Parkway., Wilsonville OR 97070 Exhibit 10.14 T: 855-423-9920 www.essinc.com OFFER LETTER October 31, 2022 Anthony Rabb Dear Anthony, As discussed, we are extending to you an offer of employment as Chief Financial Officer, reporting to Eric Dresselhuys with a start date of November 1, 2022. Compensation: •Your annual salary will be $415,000, paid out on a bi-monthly basis of $17,291.67 •As

March 2, 2023 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2022 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-395

March 2, 2023 EX-10.9

2021 Equity Incentive Plan and form of award agreements thereunder

ESS TECH, INC. 2021 EQUITY INCENTIVE PLAN 1.Purposes of the Plan. The purposes of this Plan are: •to attract and retain the best available personnel for positions of substantial responsibility, •to provide additional incentive to Employees, Directors and Consultants, and •to promote the success of the Company’s business. The Plan permits the grant of Incentive Stock Options, Nonstatutory Stock Opt

March 1, 2023 8-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 1, 2023 ESS TECH, INC. (Exa

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 1, 2023 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (

March 1, 2023 EX-99.1

ESS Tech, Inc. Announces Fourth Quarter and Full Year 2022 Financial Results Record Unit Deliveries in Q4 Ended Full Year 2022 with Almost 800 MWhs of Annual Production Capacity

Exhibit 99.1 ESS Tech, Inc. Announces Fourth Quarter and Full Year 2022 Financial Results Record Unit Deliveries in Q4 Ended Full Year 2022 with Almost 800 MWhs of Annual Production Capacity WILSONVILLE, OREGON – March 1, 2023 – ESS Tech, Inc. (“ESS,” “ESS, Inc.” or the “Company”) (NYSE:GWH), a leading manufacturer of long-duration energy storage systems for commercial and utility-scale applicatio

February 13, 2023 SC 13G/A

STWO / ACON S2 Acquisition Corp. Class A / ACON S2 Sponsor, L.L.C. - SC 13G/A Passive Investment

SC 13G/A 1 d426911dsc13ga.htm SC 13G/A UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 SCHEDULE 13G UNDER THE SECURITIES EXCHANGE ACT OF 1934 (Amendment No. 2)* ESS Tech, Inc. (Name of Issuer) Common Stock, $0.0001 par value per share (Title of Class of Securities) 26916J106 (CUSIP Number) December 31, 2022 (Date of Event Which Requires Filing of this Statement) Check the A

February 9, 2023 SC 13G/A

STWO / ACON S2 Acquisition Corp. Class A / FMR LLC Passive Investment

SCHEDULE 13G Amendment No.1 ESS TECH INC CLASS A COMMON STOCK Cusip #26916J106 Check the appropriate box to designate the rule pursuant to which this Schedule is filed: [x] Rule 13d-1(b) [ ] Rule 13d-1(c) [ ] Rule 13d-1(d) Cusip #26916J106 Item 1: Reporting Person - FMR LLC Item 2: (a) [ ] (b) [ ] Item 4: Delaware Item 5: 787,705 Item 6: 0 Item 7: 787,895 Item 8: 0 Item 9: 787,895 Item 11: 0.441%

February 6, 2023 SC 13G/A

STWO / ACON S2 Acquisition Corp. Class A / BASF Venture Capital GmbH - SC 13G/A Passive Investment

SC 13G/A 1 d304574dsc13ga.htm SC 13G/A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2)* ESS Tech, Inc. (Name of Issuer) Common stock, par value $0.0001 per share (Title of Class of Securities) 26916J106 (CUSIP Number) February 2, 2023 (Date of Event Which Requires Filing of this Statement) Check the ap

January 30, 2023 SC 13G/A

STWO / ACON S2 Acquisition Corp. Class A / Pangaea Ventures Fund III, LP - SC 13G/A Passive Investment

SC 13G/A 1 d414413dsc13ga.htm SC 13G/A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 (Amendment No. 2)* ESS Tech, Inc. (Name of Issuer) common stock, par value $0.0001 per share (Title of Class of Securities) 26916J106 (CUSIP Number) December 31, 2022 (Date of Event Which Requires Filing of this Statement) Check the a

November 25, 2022 8-K

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 25, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

November 17, 2022 424B3

130,044,756 Shares of Common Stock

424B3 1 esstech-424b3.htm 424B3 Filed Pursuant to Rule 424(b)(3) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus relates to the registration of common stock, par value $0.0001 per share (“Common Stock”), of ESS Tech, Inc. as described herein. This prospectus relates to the resale from time to time by the selling stockholders described in t

November 15, 2022 CORRESP

November 15, 2022

November 15, 2022 VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance 100 F Street, N.E. Washington, D.C. 20549 Attention: Gregory Herbers Re: ESS Tech, Inc. Registration Statement on Form S-3 Filed November 3, 2022 File No. 333-268138 Acceleration Request Requested Date: November 17, 2022 Requested Time: 4:30 p.m. (Eastern Time) Ladies and Gentlemen: Pursuant to Rule

November 10, 2022 LETTER

LETTER

United States securities and exchange commission logo November 10, 2022 Amir Moftakhar Chief Financial Officer ESS Tech, Inc.

November 3, 2022 EX-FILING FEES

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Table Form S-3 (Form Type) ESS TECH, INC. (Exact Name of Registrant as Specified in its Charter) Table 1 - Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered(1)(2) Proposed Maximum Offering Price Per Security(3)(4) Maximum Aggregate Offering Price(4) Fee Rate Amount of Registration Fee Equity Common Stock, par

November 3, 2022 EX-99.1

ESS Tech, Inc. Announces Third Quarter 2022 Financial Results Appoints Anthony Rabb as CFO

Exhibit 99.1 ESS Tech, Inc. Announces Third Quarter 2022 Financial Results Appoints Anthony Rabb as CFO WILSONVILLE, Ore. ? November 3, 2022 ? ESS Tech, Inc. (?ESS,? ?ESS, Inc.? or the ?Company?) (NYSE:GWH), a leading manufacturer of long-duration iron flow batteries for commercial and utility-scale energy storage applications, today announced financial results for its third quarter of 2022 ended

November 3, 2022 8-K

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): November 3, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

November 3, 2022 EX-4.3

Warrant to Purchase Stock, dated September 16, 2022, by and between the Company and Sacramento Municipal Utility District

Certain information has been omitted from this exhibit in places marked ?[***]? because it contains personally identifiable information omitted from this exhibit pursuant to Item 601(a)(6) under Regulation S-K.

November 3, 2022 EX-4.3

Form of Indenture

Exhibit 4.3 ESS TECH, INC. INDENTURE Dated as of , 20 [] Trustee TABLE OF CONTENTS Page ARTICLE I DEFINITIONS AND INCORPORATION BY REFERENCE 1 Section 1.1 Definitions 1 Section 1.2 Other Definitions 6 Section 1.3 Incorporation by Reference of Trust Indenture Act 6 Section 1.4 Rules of Construction 6 ARTICLE II THE SECURITIES 7 Section 2.1 Issuable in Series 7 Section 2.2 Establishment of Terms of

November 3, 2022 EX-3.2

Amended and Restated Bylaws of ESS

AMENDED AND RESTATED BYLAWS OF ESS TECH, INC. (effective October 20, 2022) TABLE OF CONTENTS Page ARTICLE I - CORPORATE OFFICES 1 1.1 REGISTERED OFFICE 1 1.2 OTHER OFFICES 1 ARTICLE II - MEETINGS OF STOCKHOLDERS 1 2.1 PLACE OF MEETINGS 1 2.2 ANNUAL MEETING 1 2.3 SPECIAL MEETING 1 2.4 ADVANCE NOTICE PROCEDURES 2 2.5 NOTICE OF STOCKHOLDERS? MEETINGS 10 2.6 QUORUM 10 2.7 ADJOURNED MEETING; NOTICE 11

November 3, 2022 S-3

As filed with the Securities and Exchange Commission on November 3, 2022

As filed with the Securities and Exchange Commission on November 3, 2022 Registration No.

November 3, 2022 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file numbe

November 3, 2022 POS AM

As filed with the Securities and Exchange Commission on November 3, 2022

As filed with the Securities and Exchange Commission on November 3, 2022 Registration No.

October 27, 2022 424B3

130,044,756 Shares of Common Stock

PROSPECTUS SUPPLEMENT NO. 4 Filed Pursuant to Rule 424(b)(3) (to prospectus dated March 17, 2022) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus supplement is being filed to update and supplement the information contained in the prospectus dated March 17, 2022 (as supplemented from time to time, the ?Prospectus?), with the information con

October 24, 2022 EX-3.1

Amended and Restated Bylaws of ESS Tech, Inc. dated October 20, 2022

AMENDED AND RESTATED BYLAWS OF ESS TECH, INC. (effective October 20, 2022) TABLE OF CONTENTS Page ARTICLE I - CORPORATE OFFICES 1 1.1 REGISTERED OFFICE 1 1.2 OTHER OFFICES 1 ARTICLE II - MEETINGS OF STOCKHOLDERS 1 2.1 PLACE OF MEETINGS 1 2.2 ANNUAL MEETING 1 2.3 SPECIAL MEETING 1 2.4 ADVANCE NOTICE PROCEDURES 2 2.5 NOTICE OF STOCKHOLDERS? MEETINGS 10 2.6 QUORUM 10 2.7 ADJOURNED MEETING; NOTICE 11

October 24, 2022 8-K

Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): October 21, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number

August 26, 2022 424B3

130,044,756 Shares of Common Stock

PROSPECTUS SUPPLEMENT NO. 3 Filed Pursuant to Rule 424(b)(3) (to prospectus dated March 17, 2022) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus supplement is being filed to update and supplement the information contained in the prospectus dated March 17, 2022 (as supplemented from time to time, the ?Prospectus?), with the information con

August 26, 2022 8-K

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 26, 2022 (August 24, 2022) ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commi

August 12, 2022 424B3

130,044,756 Shares of Common Stock

424B3 1 a2022q2esstechincformx424b3.htm 424B3 PROSPECTUS SUPPLEMENT NO. 2 Filed Pursuant to Rule 424(b)(3) (to prospectus dated March 17, 2022) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus supplement is being filed to update and supplement the information contained in the prospectus dated March 17, 2022 (as supplemented from time to tim

August 12, 2022 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001

August 11, 2022 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): August 11, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

August 11, 2022 EX-99.1

ESS Inc. Announces Second Quarter 2022 Financial Results Achieved Revenue Recognition on Energy WarehousesTM Announces Partnership with Energy Storage Industries Asia Pacific Announces Energy Center Deal with Tampa Electric Company

Exhibit 99.1 ESS Inc. Announces Second Quarter 2022 Financial Results Achieved Revenue Recognition on Energy WarehousesTM Announces Partnership with Energy Storage Industries Asia Pacific Announces Energy Center Deal with Tampa Electric Company WILSONVILLE, OREGON ? August 11, 2022 ? ESS Tech, Inc. (?ESS,? ?ESS, Inc.? or the ?Company?) (NYSE:GWH), a leading manufacturer of long-duration iron flow

June 30, 2022 424B8

130,044,756 Shares of Common Stock

PROSPECTUS SUPPLEMENT NO. 1 Filed Pursuant to Rule 424(b)(3) and Rule 424(b)(8) (to prospectus dated March 17, 2022) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus supplement is being filed to update and supplement the information contained in the prospectus dated March 17, 2022 (as supplemented from time to time, the ?Prospectus?), with

June 2, 2022 8-K

Submission of Matters to a Vote of Security Holders

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): June 1, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

May 13, 2022 10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ? QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2022 OR ? TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 00

May 12, 2022 EX-99.1

ESS Inc. Announces First Quarter 2022 Financial Results Expanded Company Operations to European Market

Exhibit 99.1 ESS Inc. Announces First Quarter 2022 Financial Results Expanded Company Operations to European Market WILSONVILLE, OREGON ? May 12, 2022 ? ESS Tech, Inc. (?ESS,? ?ESS, Inc.? or the ?Company?) (NYSE:GWH), a U.S. manufacturer of long-duration batteries for utility-scale and commercial energy storage applications, today announced financial results for its first quarter of 2022 ended Mar

May 12, 2022 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): May 12, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number) (I

April 22, 2022 DEF 14A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

DEF 14A 1 a2022esstechincproxya.htm DEF 14A UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934 Filed by the Registrant x Filed by a party other than the Registrant o Check the appropriate box: o Preliminary Proxy Statement o Confidential, for Use of the Commission Only (as permitted b

March 30, 2022 8-K

Other Events

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): March 30, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Number)

March 17, 2022 424B3

130,044,756 Shares of Common Stock

Table of Contents Filed Pursuant to Rule 424(b)(3) Registration No. 333-263316 Registration No. 333-260693 130,044,756 Shares of Common Stock This prospectus relates to the registration of common stock, par value $0.0001 per share (?Common Stock?), of ESS Tech, Inc. as described herein. This prospectus relates to the resale from time to time by the selling stockholders described in this prospectus

March 14, 2022 LETTER

LETTER

United States securities and exchange commission logo March 14, 2022 Amir Moftakhar Chief Financial Officer ESS Tech, Inc.

March 14, 2022 CORRESP

March 14, 2022

CORRESP 1 filename1.htm March 14, 2022 VIA EDGAR U.S. Securities and Exchange Commission Division of Corporation Finance, Office of Manufacturing 100 F Street, N.E. Washington, D.C. 20549-3720 Attn: Gregory Herbers Re: ESS Tech, Inc. Registration Statement on Form S-1 (File No. 333-263316) Acceleration Request Requested Date: March 16, 2021 Requested Time: 4:30 P.M. Eastern Time Ladies and Gentlem

March 4, 2022 10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) x ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2021 OR o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-395

March 4, 2022 EX-FILING FEES

Filing Fee Table

Exhibit 107 Calculation of Filing Fee Tables FORM S-1 (Form Type) ESS TECH, INC. (Exact Name of Registrant as Specified in its Charter) Table 1: Newly Registered and Carry Forward Securities Security Type Security Class Title Fee Calculation or Carry Forward Rule Amount Registered (1)(2) Proposed Maximum Offering Price Per Unit (3) Maximum Aggregate Offering Price Fee Rate Amount of Registration F

March 4, 2022 EX-FILING FEES

Filing Fee Table (filed herewith).

Exhibit 107 Calculation of Filing Fee Tables Form S-8 (Form Type) ESS Tech, Inc. (Exact name of registrant as specified in its charter) Table 1 ? Newly Registered Securities Security Type Security Class Title Fee Calculation Rule Amount Registered(1) Proposed Maximum Offering Price Per Unit Maximum Aggregate Offering Price Fee Rate Amount of Registration Fee Equity Common Stock, $0.0001 par value

March 4, 2022 S-1

As filed with the Securities and Exchange Commission on March 4, 2022

As filed with the Securities and Exchange Commission on March 4, 2022 Registration No.

March 4, 2022 S-8

As filed with the Securities and Exchange Commission on March 4, 2022

As filed with the Securities and Exchange Commission on March 4, 2022 Registration No.

February 24, 2022 EX-99.1

ESS Inc. Announces Fourth Quarter and Full Year 2021 Financial Results First Gen2 Energy Warehouse Shipped to Customer Has Been Fully Accepted and is Operational

Exhibit 99.1 ESS Inc. Announces Fourth Quarter and Full Year 2021 Financial Results First Gen2 Energy Warehouse Shipped to Customer Has Been Fully Accepted and is Operational WILSONVILLE, OREGON ? February 24, 2022 ? ESS Tech, Inc. (?ESS,? ?ESS, Inc.? or the ?Company?) (NYSE:GWH), a U.S. manufacturer of long-duration batteries for utility-scale and commercial energy storage applications, today ann

February 24, 2022 8-K

Financial Statements and Exhibits, Results of Operations and Financial Condition

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): February 24, 2022 ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (Commission File Numbe

February 17, 2022 8-K

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers, Financial Statements and Exhibits

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): February 17, 2022 (February 14, 2022) ESS TECH, INC. (Exact Name of Registrant as Specified in Charter) Delaware 001-39525 98-1550150 (State or other jurisdiction of incorporation) (C

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