From the source: A friend of mine who has someone close that works at Bungie has just been dying to tell me a secret about their future. Since the NDA officially expire today the sent me and email with the details. I have full faith in this contact. The email is as follows:
"So heres my big secret. You should google Bungie + Microsoft + separation this week.
You know that big ol BILLION dollar franchise Bungie has created for Microsoft, to show their appreciate Microsoft is letting Bungie leave. Of course Microsoft gets to keep all rights to the Halo franchise, but as today Bungie no longer part of Microsoft. Ask anyone who works there to search the global address book, they're no longer in there. Microsoft was supposed to release the press release today but if they wait till the 10/6 the impact wont effect the quarterly results. However today is the actual official date and the day the NDAs expire, however you still didn't hear this from me.
Apparently MS just wants Bungie to make Halo for the rest of their natural days, and Bungie doesn't like how MS is constantly trying to "handle" everything they do; the way they market their games, the way they interact with their fans (basically the fact that they do appreciate their fans), and how stingie they are with the profits (comparable to the rest of the industry). So as of today they are their own independent entity. They'll probably make Halo 4 for Microsoft, however hey are also free to create new intellectual properties for whatever system they want. (Even though they prefer the xbox platform)