We already know that Brutes will play the role of villains in Halo Infinite, led by the war chief Escharum. But it does seems like we're actually getting another faction to fight as well, as revealed in a hidden sound file in the latest Halo Waypoint update (discovered by Zach on Twitter).
It's mainly a conversation between Dr. Halsey and Master Chief, where the former says: "Right now, we are in survival mode, again. Cortana's message has spread across the galaxy, most sentient AI is siding with her."
This description does not fit the Brutes (they are basically really evil Wookies, but certainly not AI), and Master Chief might have to fight off both Cortana's AI troops as well as the Brute cohorts. Fortunately, Halsey implies in the sound-clip that Cortana might still have a weak spot for Master Chief, so there is some hope.
Sounds pretty exciting, doesn't it?