Document

424B5 1 prosupp-essincaugust2026.htm 424B5 Document

As filed pursuant to Rule 424(b)(5)

Registration No. 333-291506

PROSPECTUS SUPPLEMENT

(To Prospectus dated December 11, 2025)

6,400,000 Shares of Common Stock

We are offering 6,400,000 shares of our common stock, par value $0.0001 per share to certain purchasers pursuant to this prospectus supplement and the accompanying prospectus. The purchase price of each share of common stock is $0.50. The securities are being sold in this offering to certain purchasers under a securities purchase agreement dated August 20, 2026 (the “Purchase Agreement”) among us and the purchasers identified on the signature pages thereto.

In a concurrent private placement, we are also offering to the purchasers in this offering warrants to purchase up to 12,800,000 shares of our common stock (the “Common Warrants”) at an exercise price of $0.50 per share. The Common Warrants will not be exercisable until we obtain the Stockholder Approval (as defined below) and will expire five years from the date such approval is obtained. The Common Warrants and the shares of common stock issuable upon exercise of the Common Warrants are not being registered under the Securities Act of 1933, as amended (the “Securities Act”), are not being offered pursuant to this prospectus supplement and the accompanying prospectus, and are being offered in reliance upon the exemption from registration provided by Section 4(a)(2) of the Securities Act and/or Regulation D promulgated thereunder. See “Private Placement Transaction.”

We have retained Roth Capital Partners, LLC to act as exclusive placement agent (the “Placement Agent”) in connection with this offering. The Placement Agent has agreed to use its reasonable best efforts to sell the securities offered by this prospectus supplement and the accompanying prospectus. The Placement Agent has no obligation to buy any of the securities from us or to arrange for the purchase or sale of any specific number or dollar amount of securities. There is no minimum number of securities that must be sold as a condition to completion of this offering and there are no arrangements to place the funds in an escrow, trust or similar account. The Placement Agent will receive compensation in addition to the placement agent’s fees. We have also agreed to issue to the Placement Agent warrants to purchase up to 320,000 shares of common stock on the same terms as the Common Warrants, representing 5.0% of the aggregate number of shares of common stock sold in this offering (the “Placement Agent Warrants”, and together with the Common Warrants, the “Warrants”), and to indemnify the Placement Agent. See “Plan of Distribution” beginning on page S-18 of this prospectus supplement for more information regarding these arrangements.

Our common stock is listed on the New York Stock Exchange (“NYSE”) under the symbol “GWH.” The last reported sale price of our common stock on August 20, 2026 was $0.39 per share.

As of August 19, 2026, the aggregate market value of our outstanding common stock held by non-affiliates, or our public float, was approximately $30,747,387, based on 30,144,497 shares of our outstanding common stock held by non-affiliates and a price of $1.02 per share of our common stock on July 15, 2026, the highest closing price of our common stock during the preceding sixty (60) day trading period. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell our securities in a public primary offering pursuant to the registration statement of which this prospectus supplement forms a part with an aggregate market value exceeding one-third of our public float in any 12 consecutive calendar month period so long as our public float remains below $75.0 million. During the 12 calendar months prior to, and including, the date of this prospectus supplement, we have not offered and sold any securities pursuant to General Instruction I.B.6 of Form S-3, excluding the securities offered hereby.

We have agreed to pay to the Placement Agent the fees set forth in the table below, which assumes that we sell all of the securities offered by this prospectus supplement. See “Plan of Distribution” on page S-18 of this prospectus supplement for more information regarding these arrangements.


	Per Share of Common Stock		Total
Offering price	$	0.50	$	3,200,000.00
Placement Agent’s fees(1)	$	0.035	$	224,000.00
Proceeds, before expenses, to us	$	0.465	$	2,976,000.00

__________________

(1)Includes a cash fee, equal to 7.0% of the gross proceeds raised in this offering, to be paid to the Placement Agent. We have also agreed to reimburse the Placement Agent for reasonable and documented out-of-pocket legal fees and disbursements incurred by the Placement Agent not to exceed an aggregate amount of $75,000. See “Plan of Distribution” for a complete description of the compensation to which the Placement Agent is entitled. In addition, we have agreed to issue the Placement Agent Warrants to the Placement Agent. See “Plan of Distribution” and “Private Placement Transaction.”

Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page S-7 of this prospectus supplement and in the documents incorporated by reference in this prospectus supplement and the accompanying prospectus. Neither the Securities and Exchange Commission or any state securities commission has approved or disapproved of the securities being offered by this prospectus supplement or accompanying prospectus or determined if this prospectus supplement or accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the securities offered hereby is expected to be made on or about August 21, 2026, subject to satisfaction of customary closing conditions.


Roth Capital Partners

August 20, 2026

TABLE OF CONTENTS

Prospectus Supplement


			Page
About This Prospectus Supplement			S-1
Cautionary Note Regarding Forward-looking Statements			S-2
Prospectus Supplement Summary			S-3
Risk Factors			S-7
Dilution			S-11
Use of Proceeds			S-13
Description of the Securities We are Offering			S-14
Private Placement Transaction			S-15
Plan of Distribution			S-18
Legal Matters			S-21
Experts			S-21
Where You Can Find More Information			S-21
Incorporation of Certain Information by Reference			S-22

Prospectus


			Page
About this Prospectus			ii
Prospectus Summary			1
Risk Factors			4
Forward-Looking Statements			5
Use of Proceeds			6
Description of Capital Stock			7
Description of Debt Securities			8
Description of Depositary Shares			16
Description of Warrants			19
Description of Subscription Rights			20
Description of Purchase Contracts			21
Description of Units			22
Plan of Distribution			23
Legal Matters			26
Experts			26
Where You Can Find More Information			26
Incorporation by Reference			26

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the Securities and Exchange Commission (the “SEC”), utilizing a “shelf” registration process. The document is in two parts. The first part is the prospectus supplement, which describes the specific terms of this offering. The second part is the prospectus, which provides more general information about securities we may offer from time to time, some of which may not apply to this offering. Generally, when we refer to this “prospectus,” we are referring to both parts of this document combined. We urge you to carefully read this prospectus supplement and the prospectus, and the documents incorporated by reference herein and therein, before buying any of the securities being offered under this prospectus supplement. This prospectus supplement may add or update information contained in the prospectus and the documents incorporated by reference therein. As a result:

•to the extent that any statement we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference therein that were filed before the date of this prospectus supplement, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying prospectus and such documents incorporated by reference therein;

•any statement contained in a document incorporated by reference in this prospectus supplement or the accompanying prospectus that is inconsistent with information in a document incorporated by reference herein or therein that we filed on an earlier date will be deemed to modify and supersede the statement in the document filed on the earlier date; and

•any information that we file with the SEC incorporated by reference into this prospectus supplement after the date hereof will automatically update and supersede the information herein.

You should rely only on the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus, or contained in any free writing prospectus prepared by or on our behalf. We have not, and the Placement Agent has not, authorized anyone to provide you with different information. This prospectus supplement is an offer to sell only the securities offered hereby, and only under circumstances and in jurisdictions where it is lawful to do so. The distribution of this prospectus supplement and sale of these securities in certain jurisdictions may be restricted by law. Persons in possession of this prospectus supplement or the accompanying prospectus are required to inform themselves about and observe any such restrictions. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents, regardless of the date of delivery of this prospectus supplement or the accompanying prospectus, or the date of sale of any security.

We further note that the representations, warranties, and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

This prospectus supplement and the information incorporated herein by reference contain summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus supplement is a part, and you may obtain copies of those documents as described below under the heading “Where You Can Find More Information.”

Throughout this prospectus supplement, the terms “ESS,” “we,” “us,” “our” and the “Company” refer to ESS Tech, Inc., a Delaware corporation.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein contain certain statements that constitute “forward-looking statements” within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The words “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect,” “could,” “would,” “project,” “plan,” “potentially,” “likely,” and similar expressions and variations thereof are intended to identify forward-looking statements but are not the exclusive means of identifying such statements. Those statements appear in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein by reference, particularly in the sections titled “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and include statements regarding the intent, belief or current expectations of our management that are subject to known and unknown risks, uncertainties and assumptions. You are cautioned that any such forward-looking statements are not guarantees of future performance and involve risks and uncertainties, and that actual results may differ materially from those projected in the forward-looking statements as a result of various factors.

Because forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified, you should not rely upon forward-looking statements as predictions of future events. The events and circumstances reflected in the forward-looking statements may not be achieved or occur and actual results could differ materially from those projected in the forward-looking statements. Except as required by applicable law, including the securities laws of the United States and the rules and regulations of the SEC, we do not plan to publicly update or revise any forward-looking statements contained herein after we distribute this prospectus supplement, whether as a result of any new information, future events or otherwise.

In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus supplement, and although we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted a thorough inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein may contain market data that we obtain from industry sources. These sources do not guarantee the accuracy or completeness of the information. Although we believe that our industry sources are reliable, we do not independently verify the information. The market data may include projections that are based on a number of other projections. While we believe these assumptions to be reasonable as of the date of this prospectus supplement, actual results may differ from the projections.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information about us, this offering and information appearing elsewhere in this prospectus supplement and in the documents we incorporate by reference. This summary is not complete and does not contain all the information you should consider before investing in our common stock pursuant to this prospectus supplement and the accompanying prospectus. Before making an investment decision, to fully understand this offering and its consequences to you, you should carefully read this entire prospectus supplement and the accompanying prospectus, including “Risk Factors” beginning on page S-7 of this prospectus supplement and the financial statements and related notes and the other information that we incorporated by reference herein, including our most recent Annual Report on Form 10-K and our subsequently filed Quarterly Reports on Form 10-Q, which are incorporated by reference herein. Unless the context otherwise requires, all references in this prospectus supplement to “ESS,” “we,” “us,” “our,” the “Company” or similar words refer to ESS Tech, Inc.

Company Overview

ESS 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.

ESS originated in 2011 as an iron flow battery manufacturer, building upon the premise that the energy transition from a fossil fuels-based system to one dominated by renewable energy would require batteries derived from earth-abundant materials and capable of long service life. As a pioneer of iron flow technology, we developed systems to improve safety and designed for long-duration applications. More recently, ESS announced the addition of sodium-ion to its product line. Our current sodium-ion battery systems source cells from third-party suppliers. ESS manufactures and assembles the battery modules, housings, energy management systems, and other key battery components.

Today, ESS combines its expertise in long-duration iron flow batteries with next-generation sodium-ion technology and advanced energy management software. This diversified approach allows us to address a broader range of customer needs-from minutes to multiple days of energy storage-while reducing dependence on constrained critical minerals and supporting emerging domestic supply chains.

Corporate Information

Our principal executive offices are located at 26440 SW Parkway Ave., Bldg. 83, Wilsonville, Oregon, 97070, and our telephone number is (855) 423-9920. Our investor relations website is located at https://investors.essinc.com/, our Company X account is located at https://x.com/ESS_info, and our corporate LinkedIn account is located at https://www.linkedin.com/company/energy-storage-systems/. The information on, or that can be accessed through, our website and the aforementioned X account and LinkedIn account is not incorporated by reference into this prospectus supplement and should not be considered to be part of this prospectus supplement unless expressly noted. Further, our references to website URLs are intended to be inactive textual references only. We may use our investor relations website and the aforementioned X account and LinkedIn account to post important information for investors, including news releases, analyst presentations, and supplemental financial information, and as a means of disclosing material non-public information and for complying with our disclosure obligations under Regulation FD. Accordingly, investors should monitor our investor relations website and the aforementioned X account and LinkedIn account, in addition to following press releases, filings with the SEC and public conference calls and webcasts.

S-3

furnish such information with the SEC. All statements made in any of our securities filings, including all forward-looking statements or information, are made as of the date of the document in which the statement is included, and we do not assume or undertake any obligation to update any of those statements or documents unless we are required to do so by law.

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The Offering


Common Stock offered in this offering						6,400,000 shares of our common stock

Concurrent private placement						In a concurrent private placement, we are also offering to the purchasers of common stock in this offering Common Warrants to purchase up to 12,800,000 shares of our common stock at an exercise price of $0.50 per share. Additionally, we are offering the Placement Agent in this offering Placement Agent Warrants to purchase up to 320,000 shares of our common stock at an exercise price of $0.50 per share and on the same terms as the Common Warrants, except that the Placement Agent Warrants will not be exercisable until the later of (a) six (6) months after the issuance date of the Placement Agent Warrants and (b) the date on which we obtain the Stockholder Approval, and will expire five years after the issuance date of the Placement Agent Warrant. The Common Warrants will not be exercisable until we obtain the Stockholder Approval and will expire five years from the date such approval is obtained. The Warrants and the shares of common stock issuable upon exercise of the Warrants are not being registered under the Securities Act and are not being offered pursuant to this prospectus supplement and the accompanying prospectus. See “Private Placement Transaction.”

Offering Price						$0.50 per share of common stock.

Common stock to be outstanding after this offering						53,409,323 shares assuming the exercise in full of the Warrants to be issued in the concurrent private placement.

Use of proceeds						We intend to use the net proceeds from this offering for general corporate purposes, working capital and to repay approximately $1.5 million owing under our Promissory Note (as defined below) with YA II PN, Ltd. See “Use of Proceeds” in this prospectus supplement.

Risk factors						You should carefully consider the risk factors described in the section of this prospectus supplement and the accompanying prospectus titled “Risk Factors,” together with all of the other information included in or incorporated by reference into this prospectus supplement and the accompanying prospectus, before deciding to purchase our securities.

NYSE symbol						Our common stock is listed on the New York Stock Exchange under the symbol “GWH.”

Unless otherwise stated in this prospectus supplement, the number of shares of our common stock to be outstanding as of the date of this prospectus supplement and after this offering is based on 32,889,323 shares outstanding as of June 30, 2026, and excludes:

•1,058,208 shares of our common stock issuable upon the exercise of outstanding options granted under the ESS Tech, Inc. 2021 Equity Incentive Plan (the “2021 Plan”), with a weighted average exercise price of $2.07 per share;

•1,088,591 shares of our common stock issuable upon the vesting of outstanding restricted stock units granted under the 2021 Plan;

•500,855 shares of our common stock reserved for future issuance under the 2021 Plan;

•223,235 shares of our common stock reserved for future issuance under the ESS Tech, Inc. 2021 Employee Stock Purchase Plan;

•833 shares of our common stock issuable upon the exercise of a warrant issued to Sacramento Municipal Utility District, with an exercise price of $64.44 per share;

•708,775 shares of our common stock issuable upon the exercise of a warrant held by Honeywell ACS Ventures LLC (“Honeywell Ventures”), with an exercise price of $43.50 per share;

S-5

•417,997 shares of our common stock issuable upon the exercise of a warrant held by Honeywell Ventures, with an exercise price of $28.35 per share;

•51,717 shares of our common stock issuable upon the exercise of a warrant held by UOP LLC (“UOP”), with an exercise price of $21.75 per share;

•764,081 shares of our common stock issuable upon the exercise of our public warrants, with an exercise price of $172.50 per share;

•129,312 shares of our common stock issuable upon the exercise of warrants held by YA II and certain of our directors and members of our management that were issued in connection with the bridge loan, with an exercise price of $3.48 per share;

•1,052,104 shares of our common stock issuable upon the exercise of a warrant held by YA II, with an exercise price of $9.98 per share;

•2,100,000 shares of our common stock issuable upon the exercise of pre-funded warrants issued to certain institutional investors, with an exercise price of $0.00001 per share;

•12,800,000 shares of our common stock issuable upon the exercise of the Common Warrants issued to certain institutional investors, with an exercise price of $0.50 per share; and

•320,000 shares of our common stock issuable upon the exercise of the Placement Agent Warrants issued to Roth Capital Partners, LLC, with an exercise price of $0.50 per share.

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RISK FACTORS

Investing in our securities involves a high degree of risk. Our business, financial condition and results of operations could be materially and adversely affected by any of these risks. If any of these risks occur, the value of the securities we are offering in this prospectus supplement may decline and you may lose all or part of your investment. Before investing in our securities, you should consider carefully the risk factors set forth in this prospectus supplement, the accompanying prospectus and in any free writing prospectus that we have authorized for use in connection with this offering, along with the risk factors described in “Part II. Item 1A. Risk Factors” in our Quarterly Report on Form 10-Q for the fiscal quarter ended June 30, 2026 filed with the SEC on August 11, 2026 (the “Form 10-Q”) and other filings subsequently made by us with the SEC that are incorporated by reference into this prospectus supplement and the accompanying prospectus.

Sales of substantial amounts of our common stock in the public markets, or the perception that such sales could occur, could cause the market price of our common stock to drop significantly, even if our business is doing well.

Sales of a substantial number of shares of our common stock in the public market could occur at any time, including as a result of the shares sold in this offering. These sales, or the perception in the market that the holders of a large number of shares intend to sell shares, could reduce the market price of our common stock.

For example, pursuant to our shelf registration statement on Form S-3 (File No. 333-291506), of which this prospectus supplement forms a part, we may, from time to time, sell up to an aggregate of $300 million of our common stock, preferred stock, debt securities, depositary shares, warrants, subscription rights, purchase contracts, or units. We also have an at-the-market offering program pursuant to which we may offer and sell shares of our common stock having an aggregate gross sales price of up to $75,000,000. To date, we have issued 7,299,668 shares of common stock for total gross proceeds of $12.0 million under our at-the-market offering program. We have also filed, and expect to file in the future, registration statements with the SEC to register the resale of shares of our common stock by certain stockholders who have rights, subject to certain conditions, to require us to file registration statements covering their shares or to include their shares in registration statements that we may file for ourselves or other stockholders. We have also filed, and expect to file in the future, registration statements with the SEC to register shares reserved for future issuance under our equity compensation plans. Registration of these shares under the Securities Act results in the shares becoming freely tradable in the public market, subject to the restrictions of Rule 144 in the case of our affiliates.

Any issuance of securities under the shelf registration statement may cause stockholders to experience significant dilution of their ownership interests and any sales of securities by us or our stockholders under the resale registration statements could have a material adverse effect on the market price for our common stock. For example, we sold an aggregate of 6,458,634 shares of common stock at a weighted average sales price of $3.87 per share under the standby equity purchase agreement (the “SEPA”) we entered into with YA II, and we issued an additional 157,768 shares of common stock as a commitment fee under the SEPA, each of which was dilutive to our stockholders. Sales of shares of our common stock pursuant to the exercise of registration rights may make it more difficult for us to sell equity securities in the future at a time and at a price that we deem appropriate. These sales also could cause the trading price of our common stock to fall and make it more difficult for you to sell shares of our common stock at a time and price that you deem appropriate.

We may issue additional shares of common stock or preferred stock. Any such issuances would dilute the interest of our stockholders and likely present other risks.

We may issue a substantial number of additional shares of common stock or preferred stock. The issuance of additional securities:

•may significantly dilute the equity interests of our investors;

•may subordinate the rights of our stockholders if preferred stock is issued with rights senior to those afforded our common stock;

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•could cause a change in control if a substantial number of securities are issued, which may affect, among other things, our ability to use our net operating loss carry forwards, if any, and could result in the resignation or removal of our present officers and directors; and

•may adversely affect prevailing market prices for our common stock and/or warrants.

Raising additional capital may cause dilution to our stockholders, including purchasers of our common stock in this offering, restrict our operations or require us to relinquish substantial rights.

We expect to raise additional capital through the sale of equity or convertible debt securities. As a result of any such issuance, your ownership interest will be diluted, and the terms of these new securities may include liquidation or other preferences that adversely affect your rights as a common stockholder. Debt financing, if available, may involve fixed payment obligations or agreements that include covenants limiting or restricting our ability to take specific actions such as incurring additional debt, making capital expenditures or declaring dividends. If we raise additional funds through partnerships, collaborations, strategic alliances or licensing arrangements with third parties, we may have to relinquish valuable rights to our technologies, products or future revenue streams, or grant licenses on terms that are not favorable to us. We cannot assure you that we will be able to obtain additional funding if and when necessary. If we are unable to obtain adequate financing on a timely basis, we could be required to delay or scale back our development or production efforts or grant rights to develop, produce and market our products that we would otherwise prefer to develop, produce and market ourselves. In addition, we may seek additional capital due to favorable market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans.

We have discretion in the use of our cash and cash equivalents, including certain net proceeds from this offering.

Our management will have broad discretion over the use of proceeds from the sale of shares of our common stock in this offering, including for any of the purposes described in the section of this prospectus entitled “Use of Proceeds,” and could spend the proceeds in ways that do not improve our results of operations or enhance the value of our common stock. You may not agree with our decisions, and our use of the proceeds may not yield any return on your investment. Our failure to apply the net proceeds from the sale of our shares in this offering could effectively have a material adverse effect on our business, delay the development of our products, compromise our ability to pursue our business strategy, and cause the price of our common stock to decline, and we might not be able to yield a significant return, if any, on our investment of these net proceeds. In addition, the net proceeds from the sale of our shares in this offering may not be sufficient for our anticipated uses, and we may need additional resources to progress our product candidates to the stage we expect.

You will experience immediate dilution in the book value per share of the common stock you purchase.

You will incur immediate and substantial dilution as a result of this offering. The public offering price of $0.50 per share of common stock is substantially higher than the as adjusted net tangible book value per share of our common stock. If you purchase shares of common stock in this offering, you will incur immediate and substantial dilution of $0.55 per share in the as adjusted net tangible book value of shares of our common stock. As a result of the dilution to investors purchasing shares of common stock in this offering, investors may receive significantly less than the purchase price paid in this offering, if anything, in the event of liquidation. In addition, to the extent outstanding options and warrants are ultimately exercised, there will be further dilution of the securities sold in this offering.

We do not expect to declare any dividends in the foreseeable future.

We do not anticipate declaring any cash dividends to holders of our common stock in the foreseeable future. Consequently, investors may need to rely on sales of their shares after price appreciation, which may never occur, as the only way to realize any future gains on their investment.

The report of our independent registered public accounting firm includes a “going concern” explanatory paragraph.

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We will require substantial additional funds to continue our operations. Our cash, cash equivalents and short-term investments were approximately $5.6 million at July 31, 2026. Although we are expecting to be solvent following this offering, given our recurring history of losses and an insufficient amount of cash available to fund our ongoing operations for the next year, we have previously concluded that there is substantial doubt regarding our ability to continue as a going concern for a period of at least 12 months beyond the filing of our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026. Any such inability to continue as a going concern may result in our stockholders losing their entire investment. There is no guarantee that we will become profitable or secure additional financing on acceptable terms or at all, and we may not be able to raise additional capital either in this offering or otherwise. Further, the inclusion of disclosures expressing substantial doubt about our ability to continue as a going concern could materially adversely affect our stock price and our ability to raise new capital or enter into partnerships or other agreements.

We have prepared our condensed financial statements on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Our condensed financial statements included in the Quarterly Report on Form 10-Q for the quarter ended June 30, 2026 do not include any adjustments to reflect the possible inability to continue as a going concern within at least 12 months after the issuance of such financial statements.

There can be no assurance that we will be able to continue to satisfy the continued listing standards of the NYSE.

On March 24, 2025, we received a written notice from the NYSE (the “Notice”) indicating that we did not satisfy the continued listing standard set forth in Section 802.01B of the NYSE’s Listed Company Manual, as our average global market capitalization over a consecutive 30 trading-day period was less than $50 million (the “Minimum Market Capitalization Standard”) and, at the same time, our stockholders’ equity was less than $50 million. As described in the Notice, as of March 21, 2025, our 30 trading-day average global market capitalization was approximately $47.8 million and our last reported stockholders’ equity as of September 30, 2024, was approximately $49.2 million.

In accordance with applicable NYSE procedures, we timely submitted a plan to the NYSE on May 7, 2025 advising it of the definitive actions we have taken, are taking, or plan to take that we anticipate will bring us into conformity with the NYSE’s Minimum Market Capitalization Standard within 18 months of receipt of the Notice. On June 17, 2025, the NYSE observed and notified us that our then current global market capitalization was less than $15 million. Section 802.01B of the NYSE’s Listed Company Manual provides that the NYSE will promptly initiate suspension and delisting procedures if a company is determined to have an average global market capitalization over a consecutive 30 trading-day period of less than $15 million regardless of the original standard under which it listed.

On August 19, 2025, we received written notice that the NYSE’s Listings Operations Committee accepted our submission, and NYSE Regulation senior management acknowledged the acceptance. The NYSE will conduct quarterly reviews during the 18 months from our receipt of the Notice for compliance with the goals and initiatives outlined in our plan (the “Plan Period”). In addition, at the beginning of each fiscal quarter during the Plan Period, the NYSE will disclose to us any unpaid listing and annual fees owed by us to the NYSE exchange as of the end of the most recently completed calendar quarter. During our Plan Period, we will not be considered to be in compliance with our plan unless we have paid in full all of the aforementioned outstanding fees.

In addition, on June 9, 2026, we received a written notice from the NYSE indicating that we did not satisfy the continued listing standard set forth in Section 802.01C of the NYSE Listed Company Manual (“Section 802.01C”), as the average closing price of our common stock was less than $1.00 per share over a consecutive 30 trading-day period. As of June 8, 2026, the 30 trading-day average closing share price of our common stock was $0.98.

Section 802.01C requires us to notify the NYSE, within 10 business days of receipt of notice, of our intent to cure this deficiency. We timely notified the NYSE on June 18, 2026 that we intend to regain compliance. Pursuant to Section 802.01C, we have a period of six months, or in certain circumstances, until we could take stockholder action at our annual meeting, following receipt of the notice to regain compliance with the minimum share price

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requirement. We can regain compliance with the minimum share price requirement at any time during the cure period if, on the last trading day of any calendar month during the cure period, we have a closing share price of at least $1.00 and an average closing share price of at least $1.00 over the 30 trading-day period ending on the last trading day of that month. If we determine to remedy the non-compliance by taking action that will require stockholder approval, we must obtain stockholder approval no later than its next annual meeting and implement such action promptly thereafter.

We intend to monitor closely the closing bid price of our common stock and to consider plans for regaining compliance with Section 802.01C, including initiating a reverse stock split. While we plan to review all available options, there can be no assurance that we will be able to regain compliance with the applicable rules during the cure period, any subsequent extension period, or at all.

If we (1) fail to comply with our plan or do not meet the NYSE’s Minimum Market Capitalization Standard at the end of the applicable cure period, (2) are determined to have an average global market capitalization over a consecutive 30 trading-day period of less than $15 million, or (3) do not pay all outstanding fees within 45 days of the quarterly disclosure of any such fees and prior to the completion of our Plan Period, we will be subject to NYSE’s prompt initiation of suspension and delisting procedures.

If the NYSE delists our securities from trading on its exchange and we are not able to list such securities on another national securities exchange, we expect such securities could be quoted on an over-the-counter market. If this were to occur, we and our stockholders could face significant material adverse consequences including:

•a limited availability of market quotations for our securities;

•reduced liquidity for our securities;

•a determination that our common stock is a “penny stock” which would require brokers trading in the common stock to adhere to more stringent rules, possibly resulting in a reduced level of trading activity in the secondary trading market for our shares of common stock;

•a limited amount of news and analyst coverage;

•a decreased ability or even an inability to issue additional securities or obtain additional financing in the future, including pursuant to our at-the-market offering; and

•an impairment of our ability to provide equity incentives to our employees.

In the event of a delisting, we can provide no assurance that any action taken by us to restore or otherwise meet compliance with listing requirements would allow our securities to become listed again, stabilize the market price or improve the liquidity of our securities, or prevent future non-compliance with the NYSE’s or another exchange’s listing requirements.

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DILUTION

If you invest in our common stock, your interest will be diluted to the extent of the difference between the public offering price per share and the adjusted net tangible book value per share of our common stock after this offering.

The net tangible book value of our common stock as of June 30, 2026 was approximately $(5.2) million, or approximately $(0.16) per share. Net tangible book value per share represents the amount of our total tangible assets, excluding goodwill and intangible assets, less total liabilities, divided by the total number of shares of our common stock outstanding. Dilution per share to new investors represents the difference between the amount per share paid by purchasers for each share of common stock in this offering and the net tangible book value per share of our common stock immediately following the completion of this offering.

After giving effect to the issuance and sale of 916,065 shares of common stock pursuant to the Company’s “at-the-market” offering program under a sales agreement with Yorkville Ives & Co., LLC (formerly Yorkville Securities, LLC) and Roth Capital Partners, LLC (the “Existing ATM”) in the period following June 30, 2026 for aggregate gross proceeds of approximately $0.6 million, and after deducting the related fees and estimated offering expenses payable by us, the pro forma net tangible book value of our common stock as of June 30, 2026 would have been approximately $(4.6) million, or approximately $(0.14) per share.

After giving further effect to the sale of 6,400,000 shares of our common stock at an offering price of $0.50 per share, and after deducting estimated commissions and estimated offering expenses, our as-adjusted net tangible book value as of June 30, 2026 would have been approximately $(2.1) million, or approximately $(0.05) per share. This represents an immediate increase in net tangible book value of approximately $0.11 per share to our existing stockholders and an immediate dilution in as-adjusted pro forma net tangible book value of approximately $0.55 per share to purchasers of our common stock in this offering, as illustrated by the following table:


Offering price per share			$	0.50
Net tangible book value per share as of June 30, 2026	$	(0.16)
Increase per share attributable to this offering	$	0.11
As-adjusted pro forma net tangible book value per share as of June 30, 2026 after giving effect to sales under the Existing ATM			$	(0.14)
As-adjusted pro forma net tangible book value per share as of June 30, 2026, after giving effect to sales under this offering			$	(0.05)
Dilution per share to new investors participating in this offering			$	0.55

The foregoing discussion and table do not take into account further dilution to new investors that could occur upon the exercise of outstanding Warrants. The table above is based on 32,889,323 shares of our common stock outstanding as of June 30, 2026 and excludes:

•1,088,591 shares of our common stock issuable upon the vesting of outstanding restricted stock units granted under the 2021 Plan;

•500,855 shares of our common stock reserved for future issuance under the 2021 Plan;

•223,235 shares of our common stock reserved for future issuance under the ESS Tech, Inc. 2021 Employee Stock Purchase Plan;

•833 shares of our common stock issuable upon the exercise of a warrant issued to Sacramento Municipal Utility District, with an exercise price of $64.44 per share;

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