As the film was shot during the first UK lockdown in 2020, only Matthew and Tori were ever on set. The rest of the crew would review footage remotely. Ian McKellen and Conleth Hill's footage was shot by them with Matthew directing online.
Shot entirely on an iPhone as it was done during the first Uk lock down in 2020 with a crew of two.
The film is part of a larger world that the Butler-Harts have created and more of an introduction into the ideas of Infinitum than a first chapter. The main script, Infinitum, involves the experiment itself and multiple worlds (which is also being turned into a TV series and graphic novel) - Infinitum: Subject Unknown was a chance for them (during the Covid lock-down) to experiment with a few things ahead of shooting the main film and never expected it to be seen by anyone, let alone sold around the world.
According to director Matthew Butler-Hart the film was an experiment to see how far they could push an iPhone and what could be done with visual storytelling, rather than an exercise in screenwriting. He never thought that it would become what it has, especially with regards to a global audience watching it. (From an interview with British GQ magazine)
Infinitum: Subject Unknown was filmed in isolation, following government Covid guidelines.