So much for "mid-September," eh? Valve has announced that the first DLC for Portal 2, which is called "Peer Review," will be available for free download on PC, PS3, and Xbox 360 on October 4.

"Peer Review" continues the cooperative exploits of Atlas and P-Body, the two beloved robot protagonists in Portal 2's co-op campaign. GLaDOS will also be featured as the two tackle a new co-op test track. However, the DLC will also include a Challenge mode for both co-op and single-player with full leaderboard support.

To help ease the pain of waiting for free stuff, Valve's offering, uh, free stuff! You can download the third and final group of tracks from Portal 2's soundtrack, Music to Test By, right now by heading on over to Valve's site here.
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FREE PORTAL 2 DLC SHIPPING OCTOBER 4th

"Portal 2: Peer Review" Available on PC, Mac, PS3 and Xbox 360



September 29, 2011 -- 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.



Portal 2 is a hilariously mind-bending adventure that challenges you to use wits over weaponry in a funhouse of diabolical science. For more information on Steam, please visit http://www.steampowered.com.

This article was originally published on Joystiq.