Halo: Reach Multiplayer Beta
From Halopedia, the Halo wiki
The Halo: Reach Multiplayer Beta is a phase in the development of Halo: Reach, produced by Bungie Studios and organized by Microsoft. The Beta will be released to the public on May 3, 2010[1], and will be used to test different aspects of Halo: Reach multiplayer with the public, judging what to change based on public demand. An invitation to the Beta is included with all copies of Halo 3: ODST. Additionally, multiple invitations to the Beta will be randomly distributed to Xbox LIVE users by Microsoft as gifts for being loyal Xbox LIVE customers.[2]
The Beta will contain several maps and gametypes never seen before, and will showcase the new gameplay features in Reach. There will be at least a 16 player multiplayer, Theater mode has been confirmed and will be returning, but it is unknown if it will be in the Beta or not. Bungie has also stated that the Beta will include many more vehicles, leading to believe that the maps will be larger and more vehicle based. The player will also be able to use a section of the character customization to customize their Spartan, but it is not known if Elites are customizable as well.In a video of the beta you can play a mode called humans v.s. elites.