“Wednesday October 5. That will be the day in which the Portal 2 Peer Review DLC will be released. The free mission pack will extend Atlas and Peabody’s co-op adventure and add a new challenge mode for single player and co-op maps.” Click here for the full article at PC Gamer
NOTE: I also have been hearing a lot of talk about the game actually being released now and is currently playable. I have not had time to test it yet so I can’t confirm.