Perl 6 will support it's still-advancing Perl 5 big sister, and future versions of both languages will support increasing degrees of interoperability.
Perl 6 is defined by the Perl 6 test suite (which are in turn based on the Perl 6 language design documents), not by conformance to a reference implementation (as Perl 5 was).
While Perl 6 has been an infamously long time in development (see below), over the past couple of years, it has been relentlessly advancing along the long road to "industrial strength". The Rakudo Star release of Perl 6 on Parrot is due out in spring, 2010. This pre-version 1.0 release is intended to be practically usable by early Perl 6 developers.