Currently on an international press tour for Larry Crowne Hanks was on the BBC this morning and was asked bluntly if there would be a Toy Story 4. His answer? "I think there will be, yeah. Yeah, yeah, they're working on it now. There you go."
Hanks would be in a position to know, obviously, his services being required early in the process to voice Woody so this is a fairly reliable word on things. The questions, of course, are what stage of the process they're in and whether fans consider this a good thing, Toy Story 3 seeming to have been such a beautiful cap to the franchise. Continue on and you risk getting into a diminishing returns sort of situation though, of course, everybody said the same thing about making both Toy Story 2 and Toy Story 3 and we've seen how those turned out.