[1][3] The film is set in the war-torn 1940s and follows an autistic math genius Rong Jinzhen with a past shrouded in myth who is forced to abandon his academic pursuits to become a code-breaker for a secret spy agency.

[10] Liu Haoran joined the cast in September 2023,[11] followed by rumors of Tony Leung Chiu-wai and Tang Wei starring in October, though both of them denied those reports.

[18][19] Carlos Aguilar of Variety considered Decoded as "China's answer" to Christopher Nolan's Oppenheimer (2023), but criticized it for offering a sanitized and overly patriotic narrative, featuring an "uncritical depiction of China's policies and war tactics", while simultaneously demonstrating an "explicit desire to entice American sensibilities" to appease an international audience.

[20] Tay Yek Keak of 8days also compared the film to Oppenheimer in his 3/5 stars review, describing it as a blend of A Beautiful Mind (2001) and The Imitation Game (2014), but criticized it for being "too ambitious, over-plotted, and overlong" with convoluted plotlines that attempt to merge nationalistic themes with Western cultural references, while still appreciating the film's human moments and Liu Haoran's performance.

[21] Simon Abrams of RogerEbert.com gave the film 2/4 stars, describing it as a "conventional and hackneyed" spy thriller that suffers from a clichéd portrayal of a troubled mathematician and a "prevailing lack of charm and agency", rendering it "prodding" and failing to engage despite its ambitious premise.