Pyre is similar to mypy, in that it: 1. Is gradually typed, 2. Doesn't infer types, and 3. Is strict, in that it doesn't allow operations that change types.

Pyre is similar to mypy, in that it: 1. Is gradually typed, 2. Doesn't infer types, and 3. Is strict, in that it doesn't allow operations that change types. It was originally developed as a replacement for mypy that was faster and scaled better to very large codebases.