In general, I’ve concluded most ‘editions’ of pthread_self() are not the same value as this feature aims to implement. I’m not familiar enough with AIX to be certain about that platform, though. 

If there’s an equivalent function in AIX to capture the actual integral thread ID in the same 3-line way as Linux, FreeBSD, et al., are implemented (the big block in PyThread_get_thread_native_id), then it’s worth including. If the mechanism required is a more complex one than just adding a few lines, then it might be best left for a new PR. :)