The long-awaited DLC pack for Portal 2 is finally set to go live by mid-September, Valve's Doug Lombardi has confirmed at Gamescom. The free DLC was originally announced in April for a summertime release and is said to include new test chambers to solve, leaderboards, Challenge Mode for single and multiplayer, and more.

In a nod to Valve's poor track record of keeping up with their own release date estimates (there's a whole article on "Valve time" and "reverse Valve time" at the company's Developer Community site) Lombardi was quick to point out that mid-September is still technically summer -- the end of the season is marked by the autumn equinox on September 22.

Whatever the case it's hard to fault them this time around, given that the pack is completely free, and if history serves any indication it could be the first of several DLC packages that Valve releases for the game. So far they've also released the game's soundtrack and a selection of ringtones, but gamers were less enthusiastic about the paid content available on Portal 2's virtual store, which included in-game cosmetics such as gestures, hats and skins for co-op characters.

Portal 2 was released for Windows, Mac OS X, the Xbox 360, and the PlayStation 3 on April 19, 2011 in North America and on April 21, 2011 in Europe and Australia. The PC version of the game is currently selling for $30 on Steam, $20 less than its launch price just four months ago, and it includes both Mac and Windows compatibility.