Assuming that it is real, it's a safe bet that the FSB is the source - and in that case, the decision to release it is an extremely rarely made move.

Why?

Because it is as good as burning the source. It immediately reveals the type of information obtained, and identifies possible points from which it may have been obtained. Typically, information of such volume is used covertly, quietly and step-by-step, with great pains taken to mask its real source - i.e. a valuable asset.

The last time that the Russians did something so uncommon was when Rick Ames gave them a list of CIA sources in Russia. Scores of arrests and executions followed within weeks and months of obtaining that information - but that was done on the Politburo's orders, and against the recommendations (and common sense) of the KGB management.

(Ironically, it was that recklessness that saved Ames: the CIA simply could not accept the idea that the Russians had obtained the data from a mole and then acted with such disregard for that mole - so instead Langley worked on the assumption that there was no single compromising leak; if they assumed that there was a single leaker, Ames would have likely been identified much sooner than he eventually was).

What does it likely mean? Probably one of three things:

1: the source is so insignificant that it's deemed expendable - which is unlikely. Sources are protected, and this is clearly a very productive source, worth its money.

2: the FSB counts on such an earthquake in the CIA that they're assuming their source will be safe due to the chaos that follows - which would be a foolish gambit at best.

3: the source is being sacrificed for one reason: to use this leak to provide emergency assistance to a far more important, far more valuable asset. An asset like no other, perhaps the most important asset they have. Possibly the greatest and most important asset gained in the entire history of Russian secret services...