Treyarch seems to be teasing Call of Duty Warzone Zombies with in-game crossover references.
The most obvious suggestion that Warzone is getting some sort of Zombies crossover is in the Verdansk Hospital map, where players have discovered something that wasn’t there before: a janky trial machine from the Black Ops Cold War Zombies mode. You can’t interact with the machine, save for a highly suggestive text pop-up that reads “ZAI/ACTIVATE_ZOMBIES.” As Eurogamer notes, the same trial machine can be used in Black Ops Cold War Zombies to earn rewards by completing various challenges.
It isn’t clear if this was an intentional tease from Infinity Ward or an accidental preview of what’s to come. As you can see in the above tweet, the machine found in Warzone has some unfinished textures and the pop-up text looks like it could be a bit of leaked script, but this could just be Infinity Ward’s way of drumming up intrigue. Either way, it sure does seem like zombies are coming to Warzone in some way, which would fit with the overall merging of Black Ops Cold War and Warzone that’s been going on since December.