My main problem with it is that it can add a lot of extra syntax which -- while immensely useful for static checking -- is never executed in production. PEP 48

My main problem with it is that it can add a lot of extra syntax which -- while immensely useful for static checking -- is never executed in production. PEP 484 includes support for stub .pyi files, which contain the typing, but IDEs still don't take advantage of that.