Here is a press release from Gamestop on Call Of Duty Advanced Warfare Zombies.
Breaking News for Call of Duty Fans – Zombies are Back!
This just in, Zombies are back as part of the Call of Duty: Advanced Warfare season pass! Stop by any GameStop to pick up one of the most anticipated games to launch this year, along with 4-multiplayer map packs, Atlas Gorge, and yes – ZOMBIES. All this is available for purchase today GameStop as part of the Call of Duty: Advanced Warfare season pass for only $49.99.
NOTE: You don't not need the Season Pass to get the Zombie DLC. The Season Pass is just another offer to get all DLC at a discounted rate.