I don't think this is real. I mean, it's real in that it's been put into the public sphere, but it didn't come from Mueller.
Manafort has no leverage. If, as he claims, he did nothing wrong, that there was absolutely NO questionable contact between him or the campaign and the Russians, why the HELL wouldn't he walk into Mueller's office and lay it all out? Take the deal, spill everything, exonerate everyone.
The fact that he hasn't done that means he can't, because it isn't true, and Mueller has no reason to deal with him without Manafort being a cooperating witness. Mueller already knows all he needs to know from the standpoint of documents and money trails. Manafort needs a pardon, and my guess is he's upping the pressure on Trump.
I honestly believe he can't cooperate in any way with Mueller and live.
Russia may have poisoned another prominent thorn in their side yesterday, and the timing is incredibly interesting, as possible warnings go. (Yes, I admit 100% that last part--the "warning"--is a conspiracy theory from my pitiful brain, but I like it anyway.) If Manafort flips, he's going to have to go into lifetime witness protection, along with his entire family.