In a recent interview with CVG, Bungie senior designer Lars Bakken said that Halo: Reach would be their last Halo title developed for the Xbox 360:

‘In terms of a platform for Halo games made by Bungie, yes. I can’t answer that question for Microsoft though. Whether they have something in the works or not, I don’t know if they’re actually ready to talk about it yet, but in terms of Bungie-produced Halo games, ODST and then Reach is probably all you’re going to get.’

Microsoft still has the right to develop Halo games on the platform, and they most likely will until 3D television technology develops enough for their next console.