Python3 requires some code changes, but on the whole is the same language.
Perl 6 was intended to be an upgrade from 5, but over time developed into a completely new language that shared stylistic similarities to Perl 5. Perl 6 can't be compatible with Perl 5 to any large extent because XS isn't a thing anymore, so any modules that had binary parts to them can't be easily ported.
These days Perl 6 got renamed to "Raku", to signify that it's its own, independent language.
The Perl 5 line continues to exist and apparently plans for the next major version to be Perl 7.