I thought Gingrich endorsed him a long time ago and has been working closely with Trump ever since.
They’ve probably been coordinating for a long time.
It was already obvious that Newt had implicitly endorsed Trump for awhile.
As for him being VP, not sure yet. I do love Newt though, and he’s basically the only person I can think of who decisively articulates the imperative for taking on the Progressive/Left. I do think others understand it (including Trump), but nobody says it like Newt can.