User blog comment:Dragonknight86/Phineas and Ferb on Hiatus after Season 4 ends/@comment-11071310-20140216015110/@comment-1896159-20140216022008

Yep. Now they're in post production for all the episodes that have yet to air and presumably they'll carry over at least into 2015. At that point we'll probably know more about the future of the show. Honestly, with five hour long specials coming up including the Star Wars crossover as well as a bunch of other episodes that are unannounced we've got plenty of Phineas & Ferb coming.

All things considered I wouldn't be surprised to see this show come back for a 5th season. It does sound like Dan & Swampy would love to stay on board for it.