Comment by mos_basik

I know this specific example because it was one of a handful of reasons that delayed my workplace from upgrading past Python 3.5 (I think) for quite a while because of the addition of the reserved word `async`.

https://docs.python.org/3.11/whatsnew/3.5.html#pep-492-corou...

Can't speak to what GP was alluding to re: breaking semantic changes.