Paramount green-lit two sequels to this film before it even opened, because regardless of how well it would do at the box office or with critics, all film rights to the Terminator series would revert back to James Cameron in 2019. However, both sequels were canceled after the film's critical and commercial failure, paving the way for Cameron to produce Terminator: Sombre destin (2019). Unfortunately, the latter turned out to be an even bigger loss at the box office.
J.K. Simmons was stated to have improvised many of his lines. His description of a rocket to the T-800 ("Blows a door clean off. You know, for people who can't do that themselves.") even earns a stare of surprise from Arnold Schwarzenegger.
Arnold Schwarzenegger worked out for six months, about three hours a day, before shooting started, by which time he had the exact same body weight and muscle measurements as he had 12 years previously while shooting Terminator 3: La guerre des machines (2003). Coincidentally, Schwarzenegger had done the exact same thing prior to Terminator 3, which had put him on the same weight and measurements as in Terminator 2: Le jugement dernier (1991), so despite his age, his dimensions have remained fairly constant throughout the series.
Emilia Clarke became a huge fan of the Terminator franchise after being forced to watch the first two films when she was 7-8 years old by her 9-year-old brother.
The body of young Arnold Schwarzenegger in the movie (also seen in the film's first trailer) is provided by actor and bodybuilder Brett Azar. Azar won the role following an open casting call looking for a person who can match the closest to Schwarzenegger's physique in the first film. Azar never thought of the idea of being in this film until he was persuaded by his manager Mike Lyons to audition. According to Azar, aside from being judged having the closest physique (the first round of auditions involves body and muscle measurement), it was his audition video of him reenacting the Terminator's arrival at the Griffith Observatory and his perfect lip-syncing of Schwarzenegger's line, "Your clothes, give them to me. Now." at the three punks resulted in him winning the role. His face was replaced with Schwarzenegger in post-production. Schwarzenegger was Azar's bodybuilding idol and Arnold gifted him cigars and several bodybuilding magazines after the first day of shooting. He would serve this same role in the following film, Terminator: Sombre destin (2019).
Willa Taylor: (at around 55 mins) Director Alan Taylor's daughter as the young Sarah Connor in the 1970s sequences. (This is technically not a true cameo, which are by definition uncredited, and Willa is included in the credits.)