Classes of officers under GST established, listing hierarchical officer categories and provision for other appointments. Section 4 establishes the classes of officers under the Central Goods and Services Tax Act, listing a hierarchical framework from Principal Chief Commissioners/Principal Directors General through Chief Commissioners/Directors General, Principal Commissioners/Principal Additional Directors General, Commissioners/Additional Directors General, First Appellate Authority, Additional Commissioners/Additional Directors, Joint Commissioners/Joint Directors, Deputy Commissioners/Deputy Directors, Assistant Commissioners/Assistant Directors, and permitting appointment of such other classes of officers as necessary.