Michael Bay was involved from the beginning to direct this successful franchise, inspired by the comics with Autobots and Decepticons (rival robots that can easily turn into cars).
Transformers 4 will be a reboot
Transformers 4 will not be a continuation of the first three films in the series, but is operated as a reboot. The producer told us that new names will be in distribution, since no one of the original cast has signed for the project: We are excited, and the challenge is that we do a reboot and what will be, we do not know yet. It's a hybrid because there is a certain continuity and new actors will move into distribution. If someone will also be included from the original distribution, we do not know. But it will be a totally new story.
It is unlikely that Shia LaBeouf, the protagonist of the franchise, to return to the role of Sam Witwicky, especially since announced its intention to distance the character: If you had asked me 15 years ago if I will be here, I'll be answered no way. I have a great plan. I just get into movies. I'm lucky in that and I respect it. Films in which I was involved was never planned or chosen. I was 17 when I met Michael and I were "raised" by him. I learned a lot from Michael, as a person, as an actor, as a man on set. And not because I don't like working with Michael. I love working with Michael. I would make any movie he wants to do. Just that I do not think there are alternatives to Sam."