http://www.pcgamer.com/the-wolfenstein-2-freedom-chronicles-dlc-trilogy-kicks-off-in-december/

The Wolfenstein 2: The New Colossus season pass was announced in July as a three-part tale of American heroes—"Gunslinger" Joseph Stallion, Jessica Valiant, and Gerald Wilkins—undertaking to undo the Nazi war machine "from the ruins of Chicago to the vastness of space." Today Bethesda nailed its post-release plans down further by revealing two out of three release dates, and an acceptably tight window for the third. 

Technically there are four parts, as the season pass also includes Episode Zero, released the same day as the game itself, which introduces the three new characters who are not BJ Blazkowicz. But Episode Zero was also offered as a preorder bonus, and on top of that it makes a mess of the sweet trilogy styling we've come to know and love, so I'm not going to count it.