Coinciding with the release of the Halo 3: ODST content for Halo: The Master Chief Collection is a new update for the game that includes the following (in brief):

• Enabling of the Halo 3: ODST content in game
• The new Halo 2 Anniversary map “Remnant”
• Improvements to parties, matchmaking and voice chat

The update is 2.4Gb in size. To read the original post, go here. For more details about the new map and ODST content, go here.