While Dark of the Moon earned more than a billion dollars globally, outgrossing its already successful predecessors, toy sales were not as robust on the third film. Hasbro isn't too happy about that, and the thinking is that sales were down because audiences had two movies to stock up on their favorite Autobots and Decepticons. It's tough to continue selling variations on the same mechanical characters, as there only so many kids will add Energon Seltzer Blast Optimus Prime and Beach Blanket Bumblebee to their collection.
Hasbro president and CEO/Transformers producer Brian Goldner pointed out as much at the UBS Best of Americas conference, according to TFW2005. As such, the sequel will introduce a new cast of robots in disguise, all of whom will be prominently displayed at toy stores, Targets, and Wal-Marts from sea to shining sea. Goldner apparently emphasized that brands need reimagining and updating, implying that such a reinvention is in store for Transformers 4.
Hasbro also showed off a temporary logo for the fourth installment, and you can take a look at the bottom of the page. Transformers 4 is, of course, just a working title, but I'd give it even odds that someone has or will consider titling the sequel Trans4mers at some point.
Since before Dark of the Moon hit theaters, franchise star Shia LaBeouf let it be known that, with his contractual obligation done, he wouldn't be returning for the fourth movie. Bay was in the same boat, and he moved on to Pain & Gain, a dark action-comedy based on a true story of kidnapping, bodybuilding, and violence. After many a rumor, Bay committed to Transformers 4 back in February, with plans to get going on the sequel once he finishes up work on Pain & Gain.
Both Bay and producer Lorenzo di Bonaventura have asserted that this new movie is by no means a reboot. Instead, it will continue the nonsensical pseudo-story of the previous three films. When Bay's involvement was announced, the producer said, "The characters that would certainly come along would be Optimus and Bumblebee I’m sure.”
In June, Bay clarified a few points, saying the sequel, which he intends to make more cheaply than the last film, will "absolutely" be his last in the franchise. “It’s not a reboot, that’s maybe the wrong word," Bay explained at the time. "I don’t want to say reboot because then people will think we’re doing a Spider-Man and starting from the beginning. We’re not. We’re taking the story that you’ve seen — the story we’ve told in three movies already — and we’re taking it in a new direction. But we’re leaving those three as the history. It all still counts."
The fourth Transformers movie will arrive on June 29, 2014.

