As revealed about a week and half ago, the first major expansion to Battlefield 1 is now live, but only to Premium Pass holders. The DLC, They Shall Not Pass, includes 4 new maps; 2 new tanks; a new character class - the Trench Raider Elite; the Siege Howitzer stationary gun; 2 new operations; new weapons, medals, dog tags, and other unlockables; and the ability to take to the battlefield as the French army.
The Premium Pass is simply the DLC season pass bundle that will include all 4 planned Battlefield 1 DLCs. It's $50 and offers a two week headstart on each of the DLCs. So for the rest of us that means They Shall Not Pass will be going live at the end of the month.