Zach Cregger initially eyed Companion as his directorial follow-up to Barbarian (2022), though the team wound up setting the project as the directorial debut of Drew Hancock.
The name Iris is "Siri" backwards.
The opening scene of the film where Sophie Thatcher is pushing a grocery cart echoes the last scene of La fabbrica delle mogli (1975) where Katharine Ross is also pushing a grocery cart.
Kat opens Sergey's safe by entering the date of Stalin's birth (18 December 1878). The keys she presses are *181278 indicating the filmmakers' attention to details: a Russian like Sergey would use the day-month-year date format instead of the US standard month-day-year.