SCHEDULE 13G/A 0001535264-25-000047 0001535264 XXXXXXXX LIVE 1 Common Stock 06/30/2025 0001921865 ASP Isotopes Inc. 00218A105 601 PENNSYLVANIA AVENUE NW 601 PENNSYLVANIA AVENUE NW WASHINGTON DC 20004 Rule 13d-1(b) AWM Investment Company, Inc. 3931186.00 0.00 3931186.00 0.00 3931186.00 4.3 IA *AWM Investment Company, Inc., a Delaware corporation (AWM), is the investment adviser to Special Situations Cayman Fund, L.P. (CAYMAN), Special Situations Fund III QP, L.P. (SSFQP), Special Situations Private Equity Fund, L.P. (SSPE), Special Situations Technology Fund, L.P. (TECH) and Special Situations Technology Fund II, L.P. (TECH II) (CAYMAN, SSFQP, SSPE, TECH and TECH II will hereafter be referred to as the Funds). As the investment adviser to the Funds, AWM holds sole voting and investment power over 504,061 shares of Common Stock of the Issuer (the Shares) held by CAYMAN, 1,798,402 Shares held by SSFQP, 286,468 Shares held by ASP Isotopes Inc. 601 PENNSYLVANIA AVENUE NW, 601 PENNSYLVANIA AVENUE NW, WASHINGTON, DISTRICT OF COLUMBIA, 20004. AWM Investment Company, Inc., a Delaware corporation (AWM), is the investment adviser to Special Situations Cayman Fund, L.P. (CAYMAN), Special Situations Fund III QP, L.P. (SSFQP), Special Situations Private Equity Fund, L.P. (SSPE), Special Situations Technology Fund, L.P. (TECH) and Special Situations Technology Fund II, L.P. (TECH II). As the investment adviser to the Funds, AWM holds sole voting and investment power over 504,061 shares of Common Stock of the Issuer (the Shares) held by CAYMAN, 1,798,402 Shares held by SSFQP, 286,468 Shares held by SSPE, 224,765 Shares held by TECH and 1,117,490 Shares held by TECH II 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 3,931,186 4.3 AWM is the investment adviser to each of the Funds. As the investment adviser to the Funds, AWM holds sole voting power over 504,061 shares of Common Stock of the Issuer (the Shares) held by CAYMAN, 1,798,402 Shares held by SSFQP, 286,468 Shares held by SSPE, 224,765 Shares held by TECH and 1,117,490 Shares held by TECH II. Greenhouse and Stettner are members of SSCAY, the general partner of CAYMAN. Greenhouse and Stettner are members of: MGP, the general partner of SSFQP; MG, the general partner of SSPE and SSTA, the general partner of TECH and TECH II. Greenhouse and Stettner are also controlling principals of AWM 0 AWM is the investment adviser to each of the Funds. As the investment adviser to the Funds, AWM holds sole investment power over 504,061 shares of Common Stock of the Issuer (the Shares) held by CAYMAN, 1,798,402 Shares held by SSFQP, 286,468 Shares held by SSPE, 224,765 Shares held by TECH and 1,117,490 Shares held by TECH II. Greenhouse and Stettner are members of SSCAY, the general partner of CAYMAN. Greenhouse and Stettner are members of: MGP, the general partner of SSFQP; MG, the general partner of SSPE and SSTA, the general partner of TECH and TECH II. Greenhouse and Stettner are also controlling principals of AWM 0 Y 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