According to one of the Voice Actors, DC Douglas (voice of Chase), Season 4 has just finished recording, so should be showing up on (American) screens in the new year.

Just recorded my last line as "Chase" in #TFRescueBots for season 4... And maybe forever...
The cryptic quote though suggests that either this is the last season, or Chase is leaving the cast at the end of Season 4. (my thinking is the latter to freshen up the series a little, and warrant more new toys)