It sounds like not only is Manafort flipping, he's doing the uneven parallel bars, the balance beam, and the vault.
He's a new age Olga Korbut.
I'm trying to figure out why he would do this.
He could have entered a plea without cooperation that would have resulted in more jail time, but by the time he finishes serving time from his convictions from the last trial, he had a reasonable expectation that Trump would pardon him.
Now, if he is providing information implicating the "President" he threw his Get Out Of Jail Free card out the window (without getting into the chances of he himself getting thrown out a window...)
Unless Manafort thinks Trump wouldn't actually issue that pardon (which would be contrary to what we know so far) the only explanation I can think of is that Mueller's team showed him that with or without his help, there is a very good chance that Trump will not be in a position to issue any pardons in the near future.
Would you trust Trump?
NO, but then, you couldn't even have paid me to vote for the guy. Manafort worked unpaid to elect him.
Trump has a demonstrated willingness to issue politically motivated pardons, and let it be known to everyone that he was in discussions with his lawyers about pardoning Manafort. This, on top of the tweets that praised him for "staying strong" and not "flipping."
Manafort must have had a reasonable expectation that he would be pardoned. Not 100% of course, but measured against what he would be giving up without a plea that involved cooperation, I would guess a chance worth taking.
Now its possible that prosecutors never offered a plea without cooperation before this upcoming trial. But even if that is true, I would still think there is more to this.