Studio GSC Game World - the creators of S.T.A.L.K.E.R.: Shadow of Chernobyl, Clear Sky, and Call of Pripyat announced S.T.A.L.K.E.R. 2 a while ago, in 2010. But the devs didn't have a chance to finish that project as founder Sergiy Grygorovych shut GSC down in 2011. In the meantime, ex-GSC employees formed their own studio, Vostok Game and even managed to launch a free-to-play game Survarium.
In 2014, GSC suddenly returned to the world of the living, but that return was only partially successful at the Ukrainian studio's Cossacks 3 has failed to win players' hearts with "mixed or average" reviews.
Despite the troubles, GSC is all about looking to the future with the (re)announcement of S.T.A.L.K.E.R. 2. This information was revealed by Grigorowicz yesterday and later confirmed by an employee of Epic Games and the creator of the SteamSpy service. It looks like GSC Game World will develop the game using Unreal Engine 4, but the S.T.A.L.K.E.R. 2 website does not mention any platforms. The newly published webpage features a "2.0.2.1." inscription, implying that S.T.A.L.K.E.R. 2 is scheduled for 2021.