Halo: The Master Chief Collection released globally today for Xbox One but has been suffering some delays when players try to match make to Multiplayer game sessions.
Some players on Halo Waypoint have confirmed they have been in Multiplayer sessions but very few with only a few games in multiple hours since the game went live.
Microsoft has issued an Xbox Live status regarding the issue – http://support.xbox.com/en-US/xbox-live-status
Xbox members, if you are having a tough time matchmaking in Halo: The Master Chief Collection, please restart your search. We are aware that some users are experiencing longer than normal matchmaking search times. We are actively working on a fix.
We at Inside Gamer have been trying to join online all morning and have so far been unsuccessful in connecting to a session.