A new rumor from multiple places is suggesting that COD 2021's co-op mode will be Zombies once again and that Treyarch is assisting development on the mode.
Coming from @CheezburgerBoyz on Twitter, this account asks Treyarch for the second year of Cold War zombies, with another account then following up and saying that they are suggesting that Treyarch is working with Sledgehammer on a Zombies mode for this year's Call of Duty game.
Keep in mind, this hasn't been confirmed right now and, as always, you should take these rumours with a grain of salt.
However, this doesn't seem too surprising as most Call of Duty games have shifted to including some kind of Zombies mode in recent years. Call of Duty studios has also begun working together on each other's games and helping one another out where needed, so all of this does seem plausible.
It isn't yet clear if this Zombies mode will be a continuation of Black Ops Cold War's or a standalone adventure.
While we wait for an official reveal of COD 2021, which is expected in Warzone Season 4, you can stay up to date with all the leaks and rumors for the game here.