Actor Glenn Morshower had this to say to Examiner last weekend at the Con X KCin Kansas City, Missouri:
"After I did the opening ceremonies for the ride, Steven Spielberg walked up to me and chatted and said 'You know we've got you set to do the fourth one and probably the fifth one on the heels of that," said on how he was approached about the new sequels. "So, I guess in December we are on our way to making 4 and 5."
Back-To-Back shooting for movies (especially sequels) is not uncommon; famous examples being Back To The Future 2 & 3, The Matrix Reloaded & The Matrix Revolutions as well as Harry Potter and the Deathly Hallows – Part 1 & Part 2.
This latest development sheds a light on the statement made by Michael Bay himself, where he said Transformers 4 is "probably" the last Transformers movie he directs.