Preferred abbreviation: ZE or L0?

All spec-mandated symbols and filenames use ze prefix. But outside the LevelZero spec, "L0" is widely used to refer to it, and sometimes it's a mix of both:

level-zero/source/lib/ze_lib.cpp

Line 46 in ea5be99

    
           std::string loaderFullLibraryPath = create_library_path(MAKE_LIBRARY_NAME( "ze_loader", L0_LOADER_VERSION), loaderLibraryPath.c_str());

Are there any guidelines on which shorthand to use when?

One of the reasons ze was chosen as the namespace prefix rather than "l0" is because both both characters "l" and "0" are ambiguous depending on font choice. You are free to use whatever shorthand you like of course.