Splitscreen co-op has been a staple of the Halo series since its introduction in 2001. However, according to the latest issue of Game Informer, Halo 5: Guardians will have up to four player co-op in its campaign, but this will be online only.
Game Informer further reported that this co-op will be available for free through an Xbox Live Silver account, taking away some of the sting. Unfortunately, this was later reported to be a miscommunication and players wanting to try out the co-op will have to pay for a Gold Account.
The reasons why 343 Industries decided to drop local multiplayer is still unknown. The prominent theory is they did so to maintain 60fps gameplay. Regardless for the reason, it is an unfortunate step away from what made the series so popular in the beginning.