For ABAP cloud-native development, SAP recommends the ABAP RESTful Application Programming Model (RAP). RAP is designed for building cloud-ready, RESTful applications and extensions in the SAP BTP ABAP environment, supporting clean core principles. According to SAP documentation, "The ABAP RESTful Application Programming Model (RAP) is the standard model for cloud-native development in ABAP." The ABAP Cloud Development Model (A) is not a specific model. The SAP S/4HANA Cloud Extensibility Model (B) refers to extensibility approaches but is not specific to ABAP cloud-native development.
Reference:
SAP Help Portal: ABAP RESTful Application Programming Model
SAP Community: ABAP Cloud Development