Epic or D5? Epic has a caustics baker in their water plugin that’s actually quite good. Caustics approximations in general have existed as long as there’s been attempts at water rendering, but most of them are crude tiling textures or light pattern trickery.
Nvidia’s real-time implementation is a little special, because it’s sort of similar to what lumen does in GI: they actually are performing photon mapping and getting information on how light would reflect and refract, but they’re accumulating, filtering, and reprojecting it in a way that’s more complex than path-tracing. It uses a lot of rasterization, but the end result is pretty exceptional and close to the ground truth.