Way back in May, Valve said that a free Portal 2 DLC was due to come out this summer. The season officially runs out on September 22, and it looks like the DLC may not be available until then. Shacknews is reporting that the free download won't hit until next month. Thankfully, it doesn't appear to be delayed.
Portal 2 players can look forward to new test chambers, challenge modes, and leader boards in the forthcoming update. If history is any indication, they can probably bet on this being one of many DLC packages Valve releases for the game. The studio has a tendency to offer new content for its own games, such as Counter-Strike, Team Fortress, and Left 4 Dead, long after others might have abandoned them to move onto the next project.
Perhaps Valve should be moving on, though. Half-Life 2: Episode 3 was supposed to come out way back in 2007, but we haven't heard a peep about it in years.