Featuring a complex transformation, essentially the front and back ends of the truck fold and converge to become Optimus Prime's legs, as much of the truck rear is connected to the robot thighs via a series of folding panels. The rear wheel cowlings feature a hinge joint in the middle of them so they do not impede his knee articulation. The rear cabin of the cab, directly connected to the smokestacks, rotate and connect to his torso and unfold into his arms. As with most mainline Movie toys, Optimus Prime features Automorph gimmicks, and due to his pricepoint has three of them. Firstly, during initial transformation, rotating his front fenders to become his heels flips the top parts of the grill to become his toes. Secondly, sliding out the double-barrel cannon in his right forearm flips out his spring-loaded Ion Blaster, which lands into place for his right hand. (The Ion Blaster can actually be popped off his forearm fairly easily, held in place by a simple clip.) Optimus' final Automorph, located in his torso, is activated by flipping the silver lever on his stomach activating a series of spring-loaded actions where the truck windows are pushed apart, and the lever between them is raised, enabling the head to spring up from the chest cavity. At this point yellow LEDs light up the chest windows and Optimus Prime's eyes, accompanied by a "powering up" sound effect.
A later prototype/mock-up was much closer to the final product but still has some noticeable differences, such as a head with much larger antennae, longer smokestacks and a front grille section that includes the rectangular section that would sport the "Freightliner" logo on the real-life truck (on the final toy, the rectangular section is part of the hinged upper section that includes the windows). It would have also been possible to attach the ion blaster to either of his shoulders.
General Hawk stated in an interview that his typical transportation in Axiom Nexus was his Convoy colleagues. As the seats of General Optimus Prime's vehicle mode were manufactured at the same location as the VAMPs of his universe, Hawk was able to find a degree of familiarity in the strange world of Axiom Nexus. Andromeda - Axiom Nexus News, 2016/05/01