There are a handful of things that fans consider synonymous with the Halo franchise, one of which is the campaign co-op. Nearly every mainline Halo installment since 2001's Halo: Combat Evolved has had co-op gameplay, which is why fans were bummed to find out that Halo Infinite would not have one at launch. The good news is that 343 Industries has promised that campaign co-op is coming to Halo Infinite eventually. Unfortunately, it appears that this eventuality is going to take a lot longer than the initially proposed May 2022 start date.
343 delayed the campaign co-op and Forge mode of Halo Infinite to focus more on the game's then-impending release. Although fans weren't exactly happy about the lengthy delay, Halo Infinite's positive reviews at launch and subsequent updates helped ease the pain. Not to mention, 343 had promised earlier that the game's campaign co-op would arrive in May 2022, just in time for the game's second season.
Now, according to 343, implementing co-op gameplay into Halo Infinite is a lot harder than they expected, so they'll need more time to make sure that the feature works flawlessly on both the Xbox One and Xbox Series S/X as well as the PC.
343 explained that part of the reason why they're having such a hard time incorporating co-op into the latest Halo game is its open world. Halo Infinite is the first open-world Halo game, which would explain why 343 isn't familiar with it yet. Although there are fans that think that 343 should just drop co-op from Halo Infinite, the studio would be risking a lot if this happened. It wasn't too long ago that 343 was on the receiving end of criticism after 2015's Halo 5: Guardians did not get split-screen co-op. In response to this, 343 guaranteed fans that this will not happen to Halo Infinite, which puts the studio in a tight spot.
It will be interesting to see how 343 will handle the ensuing backlash of delaying both co-op and Forge mode again. However, 343 knows that it needs to make up for failing to live up to the studio's earlier promise, so they released a new Arena map in Catalyst, a new BTB map named Breaker, as well as a free-for-all elimination mode for Season 2, a new Land Grab mode, and finally, the return of King of the Hill.
As for when the co-op campaign and Forge mode is scheduled for Halo Infinite, 343 revealed that the former will arrive sometime later during Season 2. Meanwhile, Forge might not be around until Season 3 in late 2022 if not early 2023.