CMSIS-RTOS2 provides following API interfaces:

CMSIS-RTOS C API v2 is the C function interface that supports dynamic object creation.
CMSIS-RTOS C API v1 is a C function API that is backward compatible with CMSIS-RTOS v1.
CMSIS-RTOS C++ API is a C++ class function API (future extension).

It is possible to intermix the different API variants in the same application and even in the same C/C++ source module. However, the functions of the CMSIS-RTOS C API v1 may be deprecated in future versions of CMSIS-RTOS.

CMSIS-RTOS2 defines also a generic system timer interface that works across the supported Arm Cortex processors:

OS Tick API is the interface to a kernel system timer.