Other Events. On August 31, 2026, Tecogen Inc. a Delaware corporation (the “Company”), and contemporaneously with the filing of this Current Report of Form 8-K, filed with the Securities and Exchange Commission (“SEC”) a Registration Statement on Form S-3 (“Registration Statement”) under the Securities Act of 1933 (as amended, “Securities Act”). The Registration Statement covers the reoffer and resale by the selling stockholders listed therein, as set forth in the Registration Statement, of a…

and Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except as expressly set forth by specific reference in such a filing. Section 7.01 - Regulation FD Disclosure

The filing details compensation and equity grants to executives, not a management change.

and Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except as expressly set forth by specific reference in such a filing. Section 7.01 - Regulation FD Disclosure

and Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except as expressly set forth by specific reference in such a filing. Section 7.01 - Regulation FD Disclosure

and Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except as expressly set forth by specific reference in such a filing. Section 7.01 - Regulation FD Disclosure

and Exhibit 99.1 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except as expressly set forth by specific reference in such a filing. Section 7.01 - Regulation FD Disclosure

Chief Financial Officer and Treasurer — Roger P. Deschenes: Mr. Roger P. Deschenes was appointed as the Chief Financial Officer and Treasurer, separating these roles from Dr. Abinand Rangesh.

Other Events On July 21, 2025, Tecogen Inc., a Delaware corporation (“Company”) , closed on a firm commitment underwritten public offering of 3,985,000 shares of common stock, $.001 par value per share, at a price to the public of $5.00 per share, including an additional 485,000 shares to cover overallotments. The net proceeds from the offering, after deducting underwriting discounts and commissions and estimated offering expenses, were approximately $18,160,750. The Company intends to use th…

Entry into a Material Definitive Agreement. On July 18, 2025, Tecogen Inc., a Delaware corporation (“Company”) , entered into an underwriting agreement (“Underwriting Agreement”) with Roth Capital Partners, LLC, as the sole manager and underwriter (“underwriter”) of an underwritten public offering (“Offering”) , pursuant to which the Company agreed to issue and sell 3,500,000 shares (“Firm Shares”) of its common stock, $.001 par value per share (“Common Stock”) , at a price to the public of $…

and Exhibit 99.01 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing. Forward-Looking Statements This press release contains “forward-looking statements” which may describe strategies, goals, outlooks or…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. On May 1, 2025, Mr. Earl R. Lewis, III, a director of Tecogen Inc. (the “Company”), converted to common stock of the Company the balance due under the promissory note dated September 18, 2024 by the Company in favor of Mr. Lewis in the original principal amount of $500,000 (the “Note”). The balance due under the Note, including accrued interest, as of May 1, 2025 was $514,148.22. The price per share used to determine the number of shares to be issue…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

Vice President of Operations — Joseph E. Gehret: Mr. Joseph E. Gehret left the Company to pursue another opportunity.

Entry into a Material Definitive Agreement. On February 28, 2025, Tecogen Inc. (“Company,” “we,” “our, ”us”) entered into a Sales and Marketing Agreement with Vertiv Corporation, an Ohio corporation (“Vertiv”), a subsidiary of Vertiv Holdings Co., a Delaware corporation (NYSE: VRT), relating to sales and marketing of Tecogen DTx Chillers (“Tecogen Chillers”) for data center cooling applications (the “Agreement”). The Agreement is effective March 1, 2025 and has a term of two years. The Agreem…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. On September 18, 2024, Tecogen Inc. (the “Company”) borrowed $500,000 from Mr. Earl R. Lewis, III, a director and shareholder of the Company, and executed a promissory note in favor of Mr. Lewis with a maturity of one year and an interest rate of 4.57% on the terms and conditions set forth therein and the Note Subscription Agreement dated October 9, 2023, as amended. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. On July 23, 2024, Tecogen Inc. (the “Company”) borrowed $500,000 from Mr. John N. Hatsopoulos, a director and principal shareholder of the Company, and executed a promissory note in favor of Mr. Hatsopoulos with a maturity of one year and an interest rate of 5.06% on the terms and conditions set forth therein and the Note Subscription Agreement dated October 9, 2023, as amended. SIGNATURES Pursuant to the requirements of the Securities Exchange Act…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

Entry into a Material Definitive Agreement. Effective May 1, 2024 Tecogen Inc. (“Tecogen”) and Aegis Energy Services LLC (“Aegis”) amended the Agreement Regarding Assignment of Certain Maintenance Agreements dated as of March 15, 2023 by and between Tecogen and Aegis, as amended, to add to the agreements assigned to Tecogen by Aegis maintenance services agreements for thirty-one (31) cogeneration units (the “Second Amendment”). The Second Amendment includes an undertaking by Aegis to use comm…

and Exhibit 99.01 to this Current Report on Form 8-K shall shall not be deemed “filed” for purposes of Section 18 of 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 expressly set forth by specific reference in such a filing.

The filing describes a new performance bonus plan for senior management, not a change in management or officer roles.

Entry into a Material Definitive Agreement. Effective February 1, 2024 Tecogen Inc. (“Tecogen”) and Aegis Energy Services LLC (“Aegis”) amended the Agreement Regarding Assignment of Certain Maintenance Agreements dated as of March 15, 2023 by and between Tecogen and Aegis to add to the agreements assigned to Tecogen by Aegis maintenance services agreements for sixteen (16) cogeneration units and two (2) chillers (the “Amendment”). The Amendment includes an undertaking by Aegis to use commerci…