forum members and GamingTalkHQ, the gamertags belong to Bungie and Microsoft employees.
X3F, the Little Sister to our Big Daddy, has been scouring the internet for information on Epsilon, even sifting through their Big Book of Greek Letters. (Epsilon is the fifth letter in the alphabet -- following alpha, beta, gamma and delta -- implying this would be a near-final build of the game.) An anonymous source tells Xbox-Scene that the Epsilon features six maps, four-player co-op for one campaign mission, saved film testing and some customization options with the games and maps.
While we can't confirm the details of Halo 3 Epsilon, would it really surprise anyone that the developer and publisher of a first-party title are playing a few deathmatches weeks before its September 25 launch date?