A reply over at reddit commenting on the implied idea that ray tracing has been used for decades an most prerendered film cg has been ray traced all along:

I remember I think it was in pixar cars, that it'd be their first use of  ray tracing in a cg movie.

>Monster University was the first true ray tracing movie from pixar
"Historically we don't use raytracing. It wasn't until Cars that we actually supported raytracing (and even then it was a haphazard and mostly broken support)"-an interview with Chris Horne at Mason Smith's blog source

>Speed 2: Cruise Control (1997)
Snow was not directly on Speed 2 but on that film the team at ILM worked on faking expensive ray tracing - ILM, fxguide.com

Most other hollywood cg has also been lacking on ray tracing use in  decades past

>Pearl Harbor (2001)
Ben Snow Nominated, Oscar: Best Effects, Visual Effects for Pearl Harbor (2001).
Shared With: Eric Brevig, John Frazier, Edward Hirsh
>So, in the rich tradition of visual effects, says Snow, "we approached the end of the 90s with a bunch of hacks. Of course ray tracing and global illumination were already in use in production and constant improvements were cropping up each year at Siggraph. But we were, and still are to an extent, in love with the look of our RenderMan renders, and were already dealing with scenes of such heavy complexity that ray tracing and global illumination were not practical solutions."- ILM, fxguide.com

Even in 2003 with hulk still ray tracing was lacking
fx guide ben snow evolution of ilm lighting source

It has basically been during the last decade - decade and a half that ray tracing has become more common rather than being sparingly used or not at all.  

I think what they were using renderman reyes, with simpler solutions for getting global illumination.
With AI frame reconstruction, and AI denoising + hardware acceleration of ray tracing, these techniques have basically provided orders of magnitude increase in performance, basically allowing ray tracing to catch up to the very recent use of true ray tracing in highly complex scenes in film, albeit at lower fidelity.

Reply over at reddit thread