There was a small update on the development of S.T.A.L.K.E.R. 2 made today via the game's official Twitter account. Instead of utilizing the X-Ray Engine, or at least a highly updated version of it, they will instead be going with Unreal Engine.
The X-Ray Engine was the 3D game engine created by GSC Game World. The engine was used to power the first three S.T.A.L.K.E.R. titles: Shadow of Chernobyl, Clear Sky, and Call of Pripyat.
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