Today Valve has announced the first DLC for Portal 2 and it will contain new test chambers, leaderboards and a challenge mode for single and co-op modes (I am guessing this is where the leaderboards part may fit in).

Valve also announced that the DLC will be free on all platforms. The most surprising part is that Microsoft are allowing it to be a free DLC on the Xbox 360 because Microsoft are notoriousness for having nearly zero free DLC on the Xbox 360.

The DLC is due out this summer.