It's official as Bungie want's to return to being an independent developer and is ready to part ways with Microsoft. The official press release can be found here http://www.bungie.net/News/content.aspx?type=news&cid=12835 after speculation was up this MTV article http://multiplayerblog.mtv.com/2007/10/03/if-it-couldnt-be-bungie-then-who-would-make-halo-4/.