Dirty Bomb (previously named Extraction (previously named Dirty Bomb)) is on Steam. Publisher Nexon America has announced that the game will be available exclusively through Valve's service. Not yet, though—at least, not yet for most people. Splash Damage's free-to-play FPS is still in closed beta.
If you're interested in what Splash Damage did after Brink, the Steam switch coincides with a lifting of the beta embargo. The game is now available to be recorded or streamed by the game's participants.
Dirty Bomb is due for public release this Summer.