According to Bungie Community Manager Brian Jarrard, Halo: Reach has been in the works since Halo 3 finished development.

“Day to day life hasn’t changed that much. We’ve been super-busy, obviously. We’ve finally been able to announce Halo: Reach, which has been in development right since the end of Halo 3.”

“Having a portion of our team working on ODST while Reach has been going full steam; we’ve been too busy right now to think about too much else. We’re just heads-down making great games. Right now that’s our focus.”

Halo: Reach is set long before Halo: Combat Evolved, before Master Chief was the only Spartan left. Bungie has not released many details on the story yet, though. The game’s out 2010.

Bungie: Halo: Reach “in development right since the end of Halo 3″ [VG247]