Thanks for sharing, this is very informative. It seems that the _CLIENTAPP variable is initialized only once the _client_ session is started, not at the early stage of the _sas_ session (meaning, in technical terms, Scope >> Kernel, though the comparison with libref assignments is not perfect). This would mean that the %check macro you provide might not work properly if launched by the autoexec or even at INITSTMT level. The _CLIENTAPP variables are created down below at a further stage of the process when SAS Studio/SAS EG is eventually available. My tests with _CLIENTAPP date back to SAS 9.2 so I am not sure if the same applies to 9.3 & 9.4 ?