ClearSign Technologies Corporation

Item 1.01 Entry into a Material Definitive Agreement. Newbridge Securities Corporation Waiver On July 21, 2026, ClearSign Technologies Corporation (the “Company”) received a waiver (the “Waiver”) from Newbridge Securities Corporation (the “Underwriter”) of certain restrictions on sales of the Company’s capital stock set forth in Section 3.16.1 of that certain Underwriting Agreement, dated as of May 28, 2026, between the Company and the Underwriter (the “Underwriting Agreement”). Pursuant to the Waiver, the Underwriter irrevocably and unconditionally waived the restrictions set forth in Section 3.16.1 of the Underwriting Agreement, including the restrictions on the Company’s ability to (a) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of capital stock of the Company or any securities convertible into or exercisable or exchangeable for shares of capital stock of the Company, (b) file or cause to be filed any registration statement with the Securities and Exchange Commission relating to the offering of any such securities, and (c) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of capital stock of the Company, in each case solely to the extent necessary to permit the Private Sale (as defined below) to Otter Capital LLC, a California limited liability company (the “Investor”), as described below in Item 1.01 of this Current Report on Form 8-K under “Stock Purchase Agreement.” The Waiver is effective as of July 21, 2026 and will continue through and including the earlier of (i) the consummation of the Private Sale and (ii) July 31, 2026. Except as expressly set forth in the Waiver, the terms and provisions of the Underwriting Agreement remain unmodified and in full force and effect. The foregoing description of the terms of the Waiver does not purport to be complete and is qualified in its entirety by the full text of the Waiver attached as Exhibit 10.1 to this Current Report on Form 8-K, which is incorporated by reference herein. Stock Purchase Agreement On July 21, 2026, in connection with the receipt of the Waiver, the Company entered into a Stock Purchase Agreement (the “Purchase Agreement”) with the Investor, an existing stockholder of the Company that, as of the date hereof, holds more than 5% of the issued and outstanding shares of the Company’s common stock, par value $0.0001 per share (the “Common Stock”), pursuant to which the Company sold and the Investor purchased 500,000 shares of Common Stock (the “Shares”) at a price per share of $3.54, for aggregate gross proceeds of $1,770,000 (the “Private Sale”). The Shares sold pursuant to the Purchase Agreement were issued as restricted securities as defined in Rule 144 of the Securities Act of 1933, as amended (the “Securities Act”), and do not contain any registration rights. The Company intends to use the net proceeds from the Private Sale for general corporate purposes, including working capital, research and development, and marketing and sales. The foregoing description of the terms of the Purchase Agreement does not purport to be complete and is qualified in its entirety by the full text of the Purchase Agreement attached as Exhibit 10.2 to this Current Report on Form 8-K, which is incorporated by reference herein.

Item 3.02 Unregistered Sales of Equity Securities. To the extent required, the disclosure under Item 1.01 above is hereby incorporated in this Item 3.02 by reference. The Shares were issued pursuant to an exemption from registration provided by Section 4(a)(2) and/or Rule 506 of Regulation D promulgated under the Securities Act because such issuance did not involve a public offering, the Investor took the Shares for investment and not resale, the Company took appropriate measures to restrict transfer, and the Investor is a sophisticated investor. The Shares are subject to transfer restrictions, and the book-entry records evidencing the securities contain an appropriate legend stating that such securities have not been registered under the Securities Act and may not be offered or sold absent registration or pursuant to an exemption therefrom. The Shares were not registered under the Securities Act and such securities may not be offered or sold in the United States absent registration or an exemption from registration under the Securities Act and any applicable state securities laws.

Item 7.01 Regulation FD Disclosure. On July 23, 2026, the Company issued a press release announcing the Private Sale. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference herein. The information provided under this Item 7.01 of this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act or the Exchange Act except as shall be expressly set forth by specific reference in such filing.