The Creator's director decided which characters were robots during post-production.
The Creator, the new film from Godzilla and Rogue One: A Star Wars Story director Gareth Edwards, pits human beings in a war with a race of robots that came from an an AI program. The trailers have shown that there will be a ton of robots featured in the film, but we recently learned that many of the actors portraying the robot characters had no idea they weren't playing humans. While the major characters in The Creator likely knew who and what their characters were, the other actors in most scenes were told to just approach everything as if they were human.
While speaking to ComicBook.com's Brandon Davis at San Diego Comic-Con, Edwards was asked about the influences of AI in the movie. As he explained what made his AI different from what we've seen in films like The Terminator, Edwards said that he instructed all of the actors to play their characters as human as possible, in order to make the robots look more natural. In post-production, he decided which characters to turn into robots and which ones to keep human.