I think you mean it's backwards *compatible*? There's definitely no change in APIs or ABIs or anything, all that changes is the order of some statements inside Python's signal handler. (We used to we write to the magic wakeup fd and then set a flag saying a signal arrived; now we do the same things but in the opposite order. I wouldn't call it zero risk, just on the general principle that signal handlers are tricksy beasts, but I think it's about as low risk as a signal handler change can be.)

AFAICT the race condition also affects twisted and tornado, though I don't think they've noticed. The main symptom is that it makes control-C handling flaky on Windows, so it's a difficult thing to test for.

I would prefer to see it backported to 3.6, but it's a weird edge case bug so the world is not going to end if the fix has to wait for 3.7.