A previous version of this film had Bill Skarsgard providing his own voiceover for his character in the style of a Mortal Kombat announcer before H. Jon Benjamin was cast for the final version; the trailer featuring Skarsgard's voiceover has mostly been scrubbed from the internet. In the original concept trailer, Boy's inner voice is taken from a cigarette commercial, with a voice similar to Sam Elliott's.
Young Boy is played by twins Cameron and Nicholas Crovetti. They play the twins of Alexander Skarsgard's character in Big Little Lies
The guitar-playing robot is The Robot from the original "Lost in Space" with slightly different head sphere.
Samara Weaving was cast as June 27, but stepped down as scheduling conflicts and replaced by Jessica Rothe.
Stuff Isaiah Mustafa (Benny) and Bill Skarsgård (Boy) starred together in IT: Chapter Two ((2019). Isaiah played Mike Hanlon and Bill played Pennywise.