Grand Theft Auto V's upcoming next-gen version might be built off of Red Dead Redemption 2's enhanced RAGE engine tech, possibly with more optimizations and upgrades.
Rockstar plans to bring GTA V to PS5 and Xbox Series X in 2021, complete with a standalone version of GTA Online. New tidbits found in GTA V's source code hints the game will be built from RDR2's excellent RAGE engine optimizations. The code was uncovered by GTA Forums user Tez2 and directly references RDR2's RAGE version.
Remember that Red Dead Redemption 2 was built from the ground up for the PS4, PS4 Pro, and Xbox family of consoles, so its RAGE engine is specifically designed to harness the power of those systems. Expect Rockstar to tweak the engine to utilize the full might of the PS5 and Xbox Series X SoCs, which include Navi 2 GPUs and Zen 2 CPUs, as well as hefty16GB GDDR6 RAM upgrades.
Neither Rockstar nor Take-Two have divulged specifics on GTA V's next-gen version. We don't know exact performance targets, features, or whether or not ray-traced visuals/shadows/lighting will be included.
Here's the only info Rockstar has released about GTA V on next-gen hardware:
"With a range of technical improvements, visual upgrades and performance enhancements, GTAV & GTA Online will take full advantage of the PS5 hardware and its new features, making the game more beautiful and more responsive than ever."