A little rumour in OXM has found it's way to the web, saying that there is a possibility Gearbox is currently developing halo 4. All of this comes after Gearbox prez has said that they are working on something bigger than big, waaay bigger than anything they have done previously, along with the fact Bungie are unwilling to just keep making Halo games.... could they have licened it out?

It's certainly possible...

Via Joystiq