When they say compatibility they largely mean C API compatibility. PyPy doesn't even try for this, and yet it's key for any real world adoption. Building on to

When they say compatibility they largely mean C API compatibility. PyPy doesn't even try for this, and yet it's key for any real world adoption. Building on top of PyPy wouldn't have helped with C API compatibility. I really hope PyPy can organize funds to hire these guys to continue working. They have accumulated massive experience on JITting the Python runtime.