Valve officially announces plans for the first DLC for Portal 2, their puzzle/platformer sequel, which will be a free release on all platforms, adding new test chambers, leaderboards, challenge modes, and more. As was revealed earlier this week, this downloadable content is expected this summer (Valve Time). Here's word:

April 29, 2011 - Valve, creators of best-selling game franchises (such as Half-Life, Left 4 Dead, Team Fortress, and Counter-Strike) and leading technologies (such as Steam and Source), today announced the first game add-on for the year's highest rated multiplatform game, Portal 2, is in development and targeted for this summer.

Portal 2 DLC #1 will offer new test chambers for players, leaderboards, challenge mode for single and multiplayer modes, and more.

Targeted for release this summer, Portal 2 DLC #1 will be offered free of charge for the PC, Mac, Xbox 360, and PS3.

Portal 2 was released April 19 and currently holds a Metacritic score of 95%, making it the top rated multiplatform game of 2011. Portal also captured the number 1 chart position in the UK, Germany, and the Nordic countries during its first week of availability, making it the fastest-selling Valve release since Half-Life 2.

A hilariously mind-bending adventure that challenges you to use wits over weaponry in a funhouse of diabolical science, Portal 2 features expansive single and cooperative multiplayer game modes.