DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	6 Months Ended
Jun. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Description of Business—ESS Tech, Inc. (“ESS” or the “Company”) develops, manufactures, and integrates non-lithium energy storage solutions. Through sodium-ion and iron flow battery technologies, ESS uses predominantly earth-abundant materials to deliver safe, reliable, and cost-effective energy storage. ESS serves utilities, independent power producers, and commercial and industrial customers with solutions that enable increased deployment of clean, resilient energy. The Company was founded in 2011 (“Legacy ESS”) and became a publicly traded company through a business combination with a special purpose acquisition company named ACON S2 Acquisition Corp. (“STWO”) which changed its name to ESS Tech, Inc. upon closing (the “Business Combination”). As a result of the Business Combination, Legacy ESS survived and became a wholly owned subsidiary of ESS Tech, Inc. On March 31, 2024, Legacy ESS merged with ESS Tech, Inc. leaving ESS Tech, Inc. as the sole remaining legal entity. Basis of Presentation—The accompanying condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Basis and Principles of Consolidation—The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Project New Horizon, LLC, which was formed in October of 2025 and is wholly owned and controlled by the Company. The subsidiary and its activity are immaterial to the results and financial position of the Company as of June 30, 2026. All intercompany accounts and transactions have been eliminated upon consolidation. Condensed Consolidated Financial Statements—The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. GAAP for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed consolidated financial statements reflect all normal and recurring adjustments that are, in the opinion of the Company’s management, necessary in order to make the condensed consolidated financial statements not misleading. Operating results for the three and six months ended June 30, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. These condensed consolidated financial statements should be read in conjunction with the financial statements and related notes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025, as filed with the SEC on March 5, 2026. Reclassifications—Certain immaterial prior year amounts have been reclassified to conform with the current year presentation. Inventory write-down and losses on noncancellable purchase commitments separately disclosed within the Statement of Cash Flows within prior periods were reclassified to Changes in inventory and Changes in accrued and other liabilities herein. This reclassification had no effect on the net cash used in operating activities. Liquidity and Capital Resources—The Company has incurred operating losses and cash outflows from operations since inception and the Company anticipates that losses will continue in the near term. During the six months ended June 30, 2026, the Company incurred net losses of $31.5 million and used $22.4 million of cash in operating activities. As of June 30, 2026, the Company had total unrestricted cash and cash equivalents of $10.8 million. The continuation of the Company as a going concern is dependent upon its ability to obtain additional debt or equity financing in the near term in order to meet its near-term operating cash flow requirements and to generate profit from its operations. Management is evaluating various strategies to obtain additional funding, which may include additional offerings of equity, issuance of debt, or other capital sources. There is no assurance that the Company will be able to generate sufficient profits or obtain such financings on acceptable terms and conditions, on the timeline required, or at all. Any such financing activities are subject to market conditions and accordingly involve factors that are outside the Company’s control. If the Company is unable to raise sufficient capital in the near term, or if financing terms are not desirable, it will not have sufficient cash and liquidity to finance its business operations and make required payments. As a result, the Company may be required to delay, reduce the scope of, limit, curtail or terminate its business activities and product development, or may be forced to cease operations, liquidate assets, or seek protection under Chapters 7 or 11 of the United States Bankruptcy Code. These uncertainties cause substantial doubt to exist as to the Company’s ability to continue as a going concern for 12 months from the issuance of these financial statements. The accompanying condensed consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. The condensed consolidated financial statements do not reflect any adjustments that might result from the outcome of this uncertainty.

Description of Business—ESS Tech, Inc. (“ESS” or the “Company”) develops, manufactures, and integrates non-lithium energy storage solutions. Through sodium-ion and iron flow battery technologies, ESS uses predominantly earth-abundant materials to deliver safe, reliable, and cost-effective energy storage. ESS serves utilities, independent power producers, and commercial and industrial customers with solutions that enable increased deployment of clean, resilient energy.

The Company was founded in 2011 (“Legacy ESS”) and became a publicly traded company through a business combination with a special purpose acquisition company named ACON S2 Acquisition Corp. (“STWO”) which changed its name to ESS Tech, Inc. upon closing (the “Business Combination”). As a result of the Business Combination, Legacy ESS survived and became a wholly owned subsidiary of ESS Tech, Inc. On March 31, 2024, Legacy ESS merged with ESS Tech, Inc. leaving ESS Tech, Inc. as the sole remaining legal entity.

Basis and Principles of Consolidation—The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Project New Horizon, LLC, which was formed in October of 2025 and is wholly owned and controlled by the Company. The subsidiary and its activity are immaterial to the results and financial position of the Company as of June 30, 2026. All intercompany accounts and transactions have been eliminated upon consolidation.

Condensed Consolidated Financial Statements—The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. GAAP for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed consolidated financial statements reflect all normal and recurring adjustments that are, in the opinion of the Company’s management, necessary in order to make the condensed consolidated financial statements not misleading. Operating results for the three and six months ended June 30, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. These condensed consolidated financial statements should be read in conjunction with the financial statements and related notes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025, as filed with the SEC on March 5, 2026.

Reclassifications—Certain immaterial prior year amounts have been reclassified to conform with the current year presentation. Inventory write-down and losses on noncancellable purchase commitments separately disclosed within the Statement of Cash Flows within prior periods were reclassified to Changes in inventory and Changes in accrued and other liabilities herein. This reclassification had no effect on the net cash used in operating activities.

Liquidity and Capital Resources—The Company has incurred operating losses and cash outflows from operations since inception and the Company anticipates that losses will continue in the near term. During the six months ended June 30, 2026, the Company incurred net losses of $31.5 million and used $22.4 million of cash in operating activities. As of June 30, 2026, the Company had total unrestricted cash and cash equivalents of $10.8 million.

The continuation of the Company as a going concern is dependent upon its ability to obtain additional debt or equity financing in the near term in order to meet its near-term operating cash flow requirements and to generate profit from its operations. Management is evaluating various strategies to obtain additional funding, which may include additional offerings of equity, issuance of debt, or other capital sources. There is no assurance that the Company will be able to generate sufficient profits or obtain such financings on acceptable terms and conditions, on the timeline required, or at all. Any such financing activities are subject to market conditions and accordingly involve factors that are outside the Company’s control. If the Company is unable to raise sufficient capital in the near term, or if financing terms are not desirable, it will not have sufficient cash and liquidity to finance its business operations and make required payments. As a result, the Company may be required to delay, reduce the scope of, limit, curtail or terminate its business activities and product development, or may be forced to cease operations, liquidate assets, or seek protection under Chapters 7 or 11 of the United States Bankruptcy Code. These uncertainties cause substantial doubt to exist as to the Company’s ability to continue as a going concern for 12 months from the issuance of these financial statements. The accompanying condensed consolidated financial statements have been prepared on a going concern basis, which