This guide describes the interface that states with Financial Alignment Initiative Demonstrations use to conduct Medicare eligibility verification and MMP enrollment submission to the CMS MARx systems. Version 4.1 of the Guide includes information on a 2nd historical inactive MBI field on all eligibility mediums, including UI eligibility screens, batch and webservice responses. Along with this new field addition, for both prior inactive MBI fields, their corresponding effective start and end dates are also provided. These changes will be implemented on Friday, July 23, 2021.