IGN has posted a short interview with the voice of Optimus Prime, Peter Cullen. There's some interesting response to the questions asked - Cullen refers to the new Predacon dragon villain, Predaking, as "phenomenal" - along with complements for his fellow cast members including Frank Welker and Steve Blum.
Where it gets interesting is the response to the question "Does this build toward a big finale for the Transformers story?" Peter Cullen replies 'I don’t think there’s ever going to be a big finale. I think, as all series go, it’s always a transformation – there’s a good word! – into another environment.
' (He might, of course, be referring to the overall nature of the franchise and how each new series takes its own direction, and not necessarily Transformers Prime specifically)
On the subject of Transformers 4, Peter Cullen does not say much - other than confirming that yes, he will be a part of it and is very much looking forward to his involvement in the production. Check out the full interview on IGN on the other side of this link