Earlier we posted that Gearbox Software (Brothers In Arms, Borderlands) was rumored to be working on Halo 4. With Bungie out of the picture, Gearbox does seem like a logical fit — the developer did do the PC version of Halo: Combat Evolved.
What's more, Gearbox boss Randy Pitchford stated in February: "I've started a new project. It's big. It's, like, look-at-our-line-up-and-imagine-something-even-bigger kind of big. I'm Directing it myself. I can't mention it publicly yet. When you find out what this is, you'll likely agree that I can't oversell this one". But that doesn't necessarily mean Gearbox is doing Halo 4. The "big" project Pitchford is talking about could be something else entirely. And Halo 4 hasn't even been announced. (Though, Microsoft would be silly not to do it.)