[davidfstr]

mypy is compiled using mypyc. It does not run as Python code.

[mzl]

The semantics of Python makes it problematic to run at speed, it is not just about interpreted vs compiled code. Give the high levels of dynamic behaviors that are allowed, a Jit (like pypy) has a higher chance of getting decent performance if the code has an underlying behavior that can be extracted.

[Sinidir]

mypy is also written in a style conducive to speed ups when compiling with mypyc