You can play the Black Ops 7 Zombies mode, called Zombies Survival on Vandorn Farm, starting on October 3 at 10 AM Pacific Time (PT). Access to Zombies Survival runs until October 7 at 10 AM PT. This includes four days of availability: two days during the Early Access period starting October 3, and two days during the Open Beta period which begins October 5. The Early Access Beta started on October 2 for pre-order and Game Pass players, but Zombies specifically becomes playable from October 3.
