The announcement of Prey 2 from yesterday stated Human Head's upcoming first-person shooter sequel "is being built on the cutting edge id tech engine from id Software," which lead to our presumption that this referred to the Tech 5 engine that will power RAGE and DOOM 4. This turns out not to be the case. There's a footnote updating IGN's story about the announcement, where they correct their own Tech 5 assumption, as it turns out the game will use a slightly less cutting edge prior version of the engine. They quote Bethesda Softworks' Pete Hines on the topic: "This game has been in development for quite a while and id Tech 5 is still in progress (until Rage ships, and probably even after). So it really wasn't an option." Thanks VG247.