The A-Shell runtime interpreter (RUN.LIT) is compatible with programs compiled under most versions of AMOS using either the 1.3 (OCMPIL.LIT) or 1.4 (COMPIL.LIT) compiler. It is not compatible with the RP files generated by BASIC Plus. On the source code side, the A-Shell compiler is compatible with all AlphaBASIC source code written for the version 1.3 compiler, and virtually all source code written for the version 1.4 compiler. (AlphaBASIC 1.4 is a moving target and thus it is difficult to claim total compatibility at any point in time, but as new statements are added to the AMOS version, they are soon added to the A-Shell version as well.) The A-Shell compiler also supports most of the BASIC Plus source code (but not the compiled object code.) See Plus Extensions in the A-Shell Development Guide for details on which BASIC Plus code is supported.

The A-Shell compiler (either COMPIL or OCMPIL) will nearly always generate the exact same RUN file, right down to the hash code, as the corresponding AMOS COMPIL and OCMPIL will. Thus, except for BASIC Plus, you have compatibility in both directions for both your source code and compiled programs.