MRI has a GIL; major alternative implementations (JRuby, Rubinius) do not.

OTOH, addressing the downsides of a GIL are not the only reasonable motivations for an alternative implementation, so there's no reason that a better-than-stock Python (or Ruby) fundamentally must remove the GIL (the current "MRI" used to be an alternative, YARV, to the old MRI, and both had GILs.)