For Developer Extensibility the S/4HANA Cloud public interface comes on top of the ABAP Platform public interface. This ABAP Platform uses the same public interface and ABAP Language Version 5 for developer extensibility.
S/4HANA releases its main CDS views, RAP facades, class-based APIs and BAdI extension points which are needed to build non-trivial custom code for the relevant S/4HANA Cloud LoBs.
Public Interface Rules and Scope
In the cloud environment, it needs to be ensured that the customer's own development activities do not harm the system and its operation. It is to be ensured that it does not affect the frequent mandatory system upgrades executed by SAP and does not require rework by the customer after each upgrade.
To meet these requirements, any tools for extensibility or custom development need to support a restricted mode, consisting of restricted syntax/functionality meaning only a subset of the available syntax elements and functions can be used. Therefore, use of released objects, that is, only explicitly released and structurally (and functionally) stable objects can be used. Hence, SAP releases these development objects as stable APIs.