I checked with a source I have who is close to Gearbox and the best info I can confirm is that Gearbox has definitely had conversations with Microsoft about doing a new "Halo" game and is very excited at the prospect. However, last my source heard, there was no deal in place. So as far as I can tell, it's quite possible Gearbox will be doing "Halo 4," (or whatever they end up calling it), but it's not a certainty yet.