Just before the Halo Reach announcement, Bungie demoed Halo 3: ODST for the first time ever. It was also announced that the game would be released on September 22nd 2009.
The demo showed “The Rookie” preparing to drop for his mission, which takes place before Halo 3. Bungie’s Joe Staten said on stage that you will be able to change from each character as a flashback. A new co-op mode was also announced for the game.