Section 421.400 - Statutory basis and scope(a)Statutory basis. This subpart implements section 1874A of the Act, which provides for the transition of the claims processing functions and operations for both Medicare Part A and Part B intermediaries and carriers to Medicare Administrative Contractors (MACs). The transition will occur between October 1, 2005, and October 1, 2011. MACs will be fully operational in distinct, nonoverlapping geographic jurisdictions by October 1, 2011.(b)Scope. This subpart specifies the requirements under which providers and suppliers will be assigned to MACs.