When does Wings of Fire return?

Wings of Fire is a series of epic dragon fantasy novels written by author Tui T. Sutherland. The series currently consists of three arcs of five books apiece, which focus on young dragons fulfilling or subverting prophecies to save their world. Each book centers on its own protagonist, whose story is told through a third person limited perspective. A fourth arc has been confirmed by Sutherland to be in the works.