It is unclear why you believe your federal SSI benefits will be ending, however you are correct in believing that you may be eligible for benefits through the California CAPI program. CAPI was created primarily to provide assistance to those persons who were disqualified from the SSI program because of the new citizenship rules but who could not take steps to become a U.S. Citizen basically because of advanced age or some other type of disability. If you are able to begin the citizenship process, I recommend that you do so. Contact the county welfare office in your community for additional information about the CAPI program.
This is not a substitute for a consultation with an attorney or advocate in your community with a background in welfare law and immigration issues.