Rebellion has released new DLC named Abaddon Asylum for Zombie Army 4: Dead War, which includes a new campaign mission, WWI Josiah Outfit, WWII Headgear Pack, MP 1940 SMG Bundle, Zombie Tank Weapon Skins, and free Left4Dead Character Pack 1 (Bill, Francis, Louis, Zoey).
I'm not a fan of how Rebellion sells DLC for Zombie Army 4: Dead War, especially the cost, so make sure to wait for a sale before buying this DLC. Or wait for the season pass to go on sale.