Halo: The Master Chief Collection owners are receiving one month of free Xbox Live Gold subscription.
All Halo: The Master Chief Collection owners who played the game online before December 19 should find their Xbox Live Gold subscription extended by one month.
343 Industries and Microsoft are rolling out this bonus now, as an apology for the shooter bundle’s egregious matchmaking problems at launch, as confirmed via a message from Xbox Live.
In addition, players will also receive an exclusive in-game nameplate and avatar, and 343 is working on adding Halo 2?s Relic map and Halo 3: ODST’s campaign to the collection for free.
All of this is due to matchmaking being broken at launch, although it's getting there now.