https://www.cnet.com/news/how-avengers-infinity-war-made-that-crazy-thanos-battle-scene/

In a bare white room in Atlanta's Pinewood Studios in 2017, special effects guy Matt Aitken held in his hands the entire script to Avengers: Infinity War. It was incredibly rare. So rare, some of the movie's biggest stars didn't have it. So rare, a Marvel representative had to supervise him.

Aitken was different. He was the VFX head supervisor of a team specifically brought on to create one of Infinity War's most pivotal scenes: the one where Thanos battles a hit squad of Marvel superheroes, including Iron Man, Spider-Man and Star-Lord.