Via the New York Times just now:

WASHINGTON — President Trump’s former national security adviser, Michael T. Flynn, will plead guilty on Friday to lying to the F.B.I. about a conversation with the Russian ambassador last December.

The plea was the latest indication that Mr. Flynn was cooperating with the special counsel’s investigation into Russia’s interference in the 2016 presidential election. Mr. Flynn was scheduled to appear in federal court in Washington at 10:30 on Friday morning.

This is huge news. He had to offer Mueller something big to get a deal.

UPDATE:

Here are the charges that were filed today.

UPDATE 2: Click for documents outlining the facts around his plea.