It was announced today at Star Wars Celebration in Orlando that the fourth season of Rebels would be the last.
In a press release, Dave Filoni said, "Star Wars Rebels will be the complete journey that it was meant to be from the very beginning. We all felt that the time was right and that the characters were at a point where their story, and their destinies, should finally be revealed. We deeply appreciate all our fans who have journeyed with the Ghost crew, and I promise Season Four will be like no other."
The teaser trailer offered a glimpse of the final season, which will be 15 episodes long. It's shorter than the previous two seasons, but the audience was assured that this was the ending planned for the Ghost Crew, and not a premature ending.
During the panel, some announcements were made. It was announced that Saw Gerrerra and Mon Mothma would be returning to the show. Then, Warwick Davis was announced to be playing Thrawn's bodyguard assassin, Rukh.
The final season of Rebels premieres this fall on Disney XD with 15 episodes.