Microsoft and more specifically their Halo division 343 Industries have launched a Twitter page called Halo Waypoint. In of the first tweets they put to rest an old rumour that Texas based Gearbox Software, best known for the Brothers in Arms series, the upcoming Borderlands, and their work on ports and expansions of the Half-Life series, are working on a game in the Halo franchise.
"For the record, Gearbox is NOT working on a Halo title for Microsoft."
There it is. No Halo game from Gearbox Software.