SCHEDULE 13G 0001535264 XXXXXXXX LIVE Common Stock 06/30/2025 0001921865 ASP Isotopes Inc. 00218A105 601 PENNSYLVANIA AVENUE NW SOUTH BUILDING, SUITE 900 WASHINGTON DC 20004 Rule 13d-1(b) AWM Investment Company, Inc. DE 619874.00 0.00 619874.00 0.00 619874.00 6.9 IA AWM Investment Company, Inc., a Delaware corporation (AWM), is the investment adviser to Special Situations Private Equity Fund, L.P. (SSPE). As the investment adviser to the Funds, AWM holds sole voting and investment power over 619,874 shares of Common Stock of the Issuer (the Shares) held by SSPE. ASP Isotopes Inc. 601 PENNSYLVANIA AVENUE NW, SOUTH BUILDING, SUITE 900, WASHINGTON, DISTRICT OF COLUMBIA, 20004 The person filing this report is AWM Investment Company, Inc., a Delaware corporation (AWM), which is the investment adviser to Special Situations Private Equity Fund, L.P., a Delaware limited partnership (SSPE), (SSPE, will hereafter be referred to as the Funds). The principal business of each Fund is to invest in equity and equity-related securities and other securities of any kind or nature. David M. Greenhouse (Greenhouse) and Adam C. Stettner (Stettner) are members of MG Advisers, L.L.C., a New York limited liability company (MG), the general partner of SSPE. Greenhouse and Stettner are also controlling principals of AWM. The principal business address for AWM is c/o Special Situations Funds, 527 Madison Avenue, Suite 2600, New York, NY 10022. AWM is a Delaware Corporation Y 619,874 6.9 AWM is the investment adviser to the Fund. As the investment adviser to the Fund, AWM holds sole voting power over 619,874 shares of Common Stock of the Issuer (the Shares) held by SSPE. Greenhouse and Stettner are members of MG, the general partner of SSPE. Greenhouse and Stettner are also controlling principals of AWM. 0 AWM is the investment adviser to the Fund. As the investment adviser to the Fund, AWM holds sole investment power over 619,874 shares of Common Stock of the Issuer (the Shares) held by SSPE. Greenhouse and Stettner are members of MG, the general partner of SSPE. Greenhouse and Stettner are also controlling principals of AWM. 0 Y N Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. AWM Investment Company, Inc. Adam Stettner 08/14/2025