Pioneer 10 and 11 already exited the solar system. They launched years before the Voyager probes.
Depends on your definition of solar system. None have reached the outer Oort cloud (the outermost objects gravitationally bound to Sol), but all have past Neptune. In this case, they are treating the heliopause (where the ambient particles change from those from the sun to those of galactic origin) as the boundary of concern.
So you can use a few definitions of the boundary of the solar system:
Past the last planet (Neptune)
Past the last gravitationally bound object
Transition into a galactic-dominated medium from a sol dominated one
Etc.