It's tricky, since only the typed part can be sped up, and there will usually be lots of back-and-forth between typed and untyped code; which requires conversio

It's tricky, since only the typed part can be sped up, and there will usually be lots of back-and-forth between typed and untyped code; which requires conversions and checks. For comparison, Racket has gradual typing which gives a speed boost when everything is typed, but can end up much slower if anything remains untyped, e.g. see figure 3 in http://www.ccis.northeastern.edu/home/types/publications/gradual-dead/pre-treatment.pdf http://www.ccis.northeastern.edu/home/types/publications/gra... Python would probably be even worse, since it's "more dynamic" than Racket; e.g. there are many hooks that can run arbitrary code (like dunder methods), and there's little encapsulation so values may get swapped out via monkey-patching at any time.