Here's an excerpt from a recent article.
"The director, by the way, says that the fourth film will include some redesign of the robots and an entirely new cast. He also said it will be his last and set the franchise up 'for the next guy.'"
This confirms what Josh Duhamel revealed in February, that the sequel will feature an all new cast, with none of the actors from Transformers, Transformers: Revenge of the Fallen, or last year's Transformers: Dark of the Moon returning. Ehren Kruger is writing the screenplay, although no story details have been given yet.
It isn't known when production will begin, although Paramount has set a June 29, 2014 release date.
Transformers: Age of Extinction was released June 27th, 2014 and stars Nicola Peltz, Mark Wahlberg, John Goodman, T.J. Miller, Stanley Tucci, Kelsey Grammer, Sophia Myles, Jack Reynor. The film is directed by Michael Bay.