In a recent interview with Examiner, Mark Wahlberg stated that Transformers 4 will start principal photography at the end of May.
Examiner: Will you have to put more weight on for “Transformers
Wahlberg: Well I took a month off – I just started working out,
I’m in my 4th week now – hopefully we’ll do “Avon Man” before “Transformers,”
which is this comedy we have at Fox that we’ve been developing; it’s kind of
like my first romantic comedy.
Examiner: Can you tell us anything
about “Transformers 4” or “Ted 2”?
Wahlberg: I could tell you that
we’re doing “Transformers” starting at the end of May, and then “Ted” in
September. You know I can’t give you too many story points or Michael will not
be happy. But I can tell you that I’m very excited, obviously I had a great
working relationship with Michael on “Pain & Gain”.
This isn't official though and it seems like lately Wahlberg has been giving us as much misinformation as Michael Bay has in the past, so take this as a grain of salt for now.