Back when Treyarch conceived of the Nazi Zombies mode for Call of Duty: World at War, they probably never suspected just how big a sensation the mode would become. Zombies have become so inseparable from CoD that they've bled over to Infinity Ward titles as well - but will they infest Warzone as well?
From their conception, Zombie modes have typically been a staple of Treyarch's entries in the series. Activision relies on two developer subsidiaries, Treyarch and Infinity Ward, to develop Call of Duty games, allowing the annual release schedule while keeping pressure off development teams, and providing some semblance of variety from release to release.
In some recent titles, the sheer popularity of Zombies led to them appearing in Infinity Ward titles as well. Modern Warfare, and by extension Warzone, are developed by Infinity Ward. There was a time when this would mean a definitive "no" to the question of Zombies, but the precedent is given.
Why would we be asking this at all, though? Beyond the popularity of Zombies modes begging the question on their own, a particularly intriguing set of easter eggs in the game have sent the community into a wild spiral of speculation, and this is the prevailing fan theory.
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Throughout Verdansk lie scattered locked bunkers. These shelters are protected by blast-doors protected by keypads, some of which can be interacted with, but players aren't sure how to open them yet. It is very likely that they will factor into some future content for Warzone, we just don't know what kind.
The keypads on these doors can be interacted with, but you can't actually enter any password. The operator simply performs a canned animation of entering a code and being denied access. The same is true of the interactable laptops spread around the map. Someone managed to glitch into the bunker using a drone, but they are empty right now.
This means that whatever plans exist for the bunkers, the content simply isn't present in the game yet. It is also possible that bunkers will work as a vault-style loot mechanic, where the contents are generated upon opening the door, hence them being empty when entered via glitch.
Games change much more dynamically these days than they did a few years ago. Games-as-a-service is the norm for multiplayer titles, and battle royale games, in particular, like to shake things up with large events and map-changing spectacles.
Verdansk is Warzone's only map and Infinity Ward is definitely working on some ideas to keep it fresh for veteran players. Some other battle royale games solved this issue by adding entirely new maps for players to shoot up, like in PlayerUnknown's BattleGrounds.
Fortnite: Battle Royale, on the other hand, stuck to its one main map that kept changing from update to update, and was then entirely reworked after it was "consumed by a black hole" in-universe.
It's possible that in an upcoming update which adds a new game mode, the bunker doors will be flung open. Many fans hope that these bunkers are hiding zombie hordes, waiting to be unleashed, but other than wishful thinking, we don't have a lot to base that on right now.
A possible direction the developers may take with this is using the bunkers and the zombies to explain Verdansk's lack of a civilian population. Modern Warfare already clears that up, but Call of Duty Zombies modes traditionally inhabit a different canon than the realistic portions of the game.
The premise is already on a silver platter right in front of us - the game gas that causes the circle collapses in Warzone and is a significant plot element in Modern Warfare has the side effect of zombifying victims in this alternate universe, and the already infected population of Verdansk holed up in the bunkers in the hopes of riding it out. Everyone became infected down there, and at some point later on an unsuspecting Operator accidentally opens up the doors.
Considering the popularity Warzone has already achieved, it's not like Infinity Ward need a high-caliber event like this to draw in players, but it's possible that the trigger will be pulled if numbers begin to plateau. With so many players discussing the possibility despite the lack of any indication it may be happening, it's clear how big a splash the mode would potentially make.