It was reported recently that 2023 would have a premium entry in the Call of Duty franchise. Due to the vagueness of this, it was assumed by many that there would simply be some DLC content coming to Call of Duty: Modern Warfare II.
However, a recent report by Insider Gaming states that while the new game may have started out as just DLC, Sledgehammer has since changed the project to be a full new Call of Duty game, complete with a campaign.
It is also said to be a large collaborative project between all of Activision's Call of Duty studios, with Sledgehammer still acting as the lead developer.
Speculation is currently pointing towards the new game being heavily connected to the Modern Warfare series, but we'll have to see if we end up with Modern Warfare 3.