For the on-premise edition of SAP S/4HANA, SAP GUI is still supported, and can be used alongside SAP Fiori applications to provide an easy transition for existing SAP customers who are familiar with the classic interface. Additionally, there are a number of transactions that are not yet converted to SAP Fiori, and SAP GUI is still needed for those. It is important to remember that very often there is not a 1:1 relationship between a classic SAP GUI transaction and an SAP Fiori application. In many cases, a single SAP Fiori application can replace many individual SAP GUI transactions.