While earlier versions had ray tracing, X16 refined the PBR camera view. Version 263010 specifically optimized the "sun follows camera" feature, preventing washing-out of interior renders. The result is photorealistic previews that update in real-time without switching to a separate render engine.
: X16 introduced significant presentation upgrades, including Physically Based Ray Tracing (PBR) chief architect premier x16 v263010 x64