My understanding from Mojo's plans is that they want to compile all of Python via their compiler (eventually), and then extend Python with extra syntax that wil

My understanding from Mojo's plans is that they want to compile all of Python via their compiler (eventually), and then extend Python with extra syntax that will compile to high performance. I think right now they might not compile all of Python yet, so you are right they are neither a subset nor a superset, but once they deliver on their plans, they will become a superset.