It's unrelated to a python TCO. It's only about new optimizations now possible with the new clang 15 musttail attribute in the inner VM loop. while op { switch op case bla: ...} to reduce register pressure in the ops. This is possible for all other dynamic language VM's also (which didn't resort to luajit's assembly vm loop).

Compilers register allocation can never better when they cannot prove TCO. With this they can skip that