GCS Game World and Valve Software have announced that the digital version of "S.T.A.L.K.E.R.: Clear Sky" will be exclusively released through Steam.

"The official prequel to the Survival FPS game S.T.A.L.K.E.R.: Shadow of Chernobyl is currently slated for simultaneous release on Steam and at retail outlets later this year.

"Steam has introduced S.T.A.L.K.E.R. to many thousands of new fans all over the world," said GSC Game World's CEO Sergiy Grygorovych. "We chose to deliver the digital version of the game exclusively on Steam because of its proven success not only as the leading global digital distribution platform for games, but because it allows us to directly reach its integrated and active community of gamers."

"It's great to see a forward-thinking game maker like GCS Game World launching simultaneously in digital and traditional retail channels," said Gabe Newell, co-founder and president of Valve. "By launching S.T.A.L.K.E.R.:Clear Sky on Steam on the same day that it's available in stores worldwide, GCS Game World ensures that gamers can get their hands on this highly-anticipated game in the way that's most convenient for them."

S.T.A.L.K.E.R.: Clear Sky brings the players one year prior to the events of the original S.T.A.L.K.E.R. game in 2011. A group of stalkers has, for the first time, reached the very heart of the Zone-Chernobyl Nuclear Power Plant-and brings about a cataclysm on the brink of a catastrophe. Through a rich narrative and gripping combat action, players uncover new challenges and insights in the Exclusion Zone. A new version of the game engine, X-Ray 1.5, powers superior graphical details and realistic and non-scripted combat AI."