> For 3.8 I can apply the same fix and make sys.base_executable public, or keep it as sys._base_executable. Either way, it'll show up in PyConfig. (Victor - thoughts here? Should be a non-breaking change, right?)

There is _PyConfig._config_version which is designed to support PyConfig change without losing ABI compatibility... but I didn't implement code for that yet :-)

If you have to modify PyConfig in 3.8, I suggest to directly use "base_executable" "public" name there (don't change it from _base_executable  to base_executable from 3.8 to 3.9, it would be painful).

I'm not sure of the purpose of sys._base_executable. Maybe open a separated issue to make the attribute public? I'm not sure if multiprocessing (for example) should use it, or if sys.executble should be used.