In the "Project Items" dialog window, click on the Folders/Extensions tab. In this section, you will see the current toolchain configuration.

Using Arm Compiler 5 is not free for all use cases, and understanding the licensing landscape is critical to avoid compilation errors.

While Keil MDK has transitioned to Arm Compiler 6 (Armclang), Version 5 is still widely used.

Many production-ready projects were written using Version 5-specific syntax, pragmas, and inline assembly that are incompatible with Version 6.

AC5 is . However:

If you have a valid Keil MDK license (including Community/Free-for-limited-size), you can install an older MDK version that still contains ARMCC: