Valve, creators of best-selling game franchises (such as Half-Life and Counter-Strike) and leading technologies (such as Steam and Source), today announced the free DLC update for its bestselling game franchise Portal 2 will be rolled out across all regions on Steam, Xbox LIVE and PSN starting October 4th. The free DLC, titled “Portal 2: Peer Review”, is available to all owners of Portal 2 for download on PS3 and Xbox 360, and will be automatically downloaded via Steam on PC and Mac.

In “Peer Review”, 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 DLC also features a single player and co-op Challenge Mode, and leaderboards to compare Challenge Mode scores with friends and the Portal community.

To hold you over until the release next week, visit http://thinkwithportals.com/ for the final installment of the Portal 2 soundtrack Music to Test By.