I think this is the key answer, de-noising, using various neural techniques finally allowed acceptable images to be produced from sometimes <1 ray / pixel, wher

I think this is the key answer, de-noising, using various neural techniques finally allowed acceptable images to be produced from sometimes <1 ray / pixel, where normally images produced at such densities were nearly unusable. This is still not perfect and many ray tracing techniques rely on accumulation over time which limits certain images from working (I imagine raytracing a small particle cloud, or fast shifting objects to be a worst case scenarios)