Vor langer Zeit angekündigt, nun steht der offizielle Releasetermin fest: Das Entwicklerteam Valve will das kostenfreie Co-op DLC-Paket zu Portal 2 am 4. Oktober 2011 für Xbox 360, PS3, PC und Mac veröffentlichen.
[quote]"Peer Review" continues the game's co-op storyline, according to Valve. "You and a friend will continue the story of loyal bots P-Body and Atlas as you puzzle your way through a mysterious new co-op test track and once again match wits with GLaDOS."
The expansion will also include single-player and co-op challenge mode that uses online leaderboards.[/quote]