Dennis Chun appeared in the sixteenth episode of the season as his Hawaii Five-0 character in a minor crossover event.

Despite Hawaii Five-0 ending in 2020, Dennis Chun still made a guest appearance in the sixteenth episode of the season as his Hawaii Five-0 character, Honolulu Police Department Sergeant Duke Lukela, after making a guest appearance in all three previous seasons of Magnum P.I.

[23] The series' writers have confirmed that it will be a full season consisting of eighteen to twenty-two episodes,[24] later stating it will be twenty.

[29] On August 27, 2021, it was announced that Chantal Thuy had been cast in an undisclosed capacity as Lia Kaleo, an HPD detective who is Katsumoto's partner and Magnum's secret girlfriend.

[30] On September 28, 2021, Martin Martinez was cast in a recurring role as Cade Jensen, a troubled teenager looking for a job at La Mariana who ends up bonding with T.C.

[31] On December 30, 2021, it was reported that Levy Tran had been cast in a guest-starring role as Tia Min, a bodyguard for a powerful crime lord.

[32] Christopher Thornton, Bobby Lee, and Jay Ali returned as Kenny "Shammy" Shamberg, Jin Jeong, and Ethan Shah, respectively, after being introduced in previous seasons.