Item 1.01. 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 issued to Mr. Lewis upon conversion of the Note to shares of Company common stock was $2.14 per share, the average closing price per share during the preceding thirty trading days. The Company issued 240,256 shares of Company common stock to Mr. Lewis as payment in full of the balance due under the Note. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Company has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized. TECOGEN INC. By: /s/ Abinand Rangesh May 2, 2025 Abinand Rangesh, Chief Executive Officer