"Trumpets please . . . Bumblebee, a 2014 Concept Camaro! . . . the final jewel in the Transformers 4 crown. High resolution image: http://bayhem.com/18tH0jv"
The reveal is well timed as the vehicle has already been spotted filming at the General Motors proving grounds facility in Michigan. Based on the above notes and select pictures from Autoblog.com, it seems the core Autobot characters are Optimus Prime (Western Star truck), Bumblebee (2014 Camaro), 2014 C7 Corvette Stingray, 2013 Bugatti Vitesse, and Hound ( Oshkosh Tactical Vehicle). The rest of the photo set is here. Thanks to Wynton R. for the link.
Update: Added the video that the pictures were taken from.