This is the first time I've learned of this. How it compares to PyPy [1]:
> PyPy is an implementation of Python with its own JIT. The biggest difference compared to Pyjion is that PyPy doesn't support all C extension modules without modification unless they use CFFI or work with the select subset of CPython's C API that PyPy does support. Pyjion also aims to support many JIT compilers while PyPy only supports their custom JIT compiler.
Apparently it's originally a Microsoft project, and it requires .NET. The project already exists for a few years, but it looks like they've gained net performance improvements over CPython only the past few months [2].
Isn't this what the GraalVM [1] guys are also trying to do? Seems like today the competition is between who is more polyglot than the other, JVM, CLR or WASM.