The working title of the series was 'Princess Maker' before it was changed to 'Sky Castle'; the original title was retained as the name of one of the drama's OST tracks.
Even before the show began broadcasting, its episode order was extended from 16 to 20 episodes, a decision producers attributed to their strong confidence in writer Yoon Hyun-mi's script and the amount of story left to explore.
Writer Yoon Hyun-mi reportedly wrote the drama drawing on her own experience of raising children through university entrance exams and her distress over news stories of students who died by suicide due to exam pressure, hoping the show might 'save at least one family.'
Kim Jung-eun was considered for a lead role (other than Han Seo-jin or Jin Jin-hee) but ultimately declined the offer.
Lee Tae-ran returned to television with this drama after a three-year hiatus caused by the earlier cancellation of an SBS daily drama that had derailed her planned comeback.
Kim Seo-hyung turned down the casting offer twice before finally accepting the role after being persuaded by director Joo Hyun-tak and her agency's CEO.
Child actress Kim Hye-yoon auditioned for both the roles of Kang Ye-seo and Kim Hye-na, and was ultimately cast as Kang Ye-seo; other young cast members were then chosen to match her age group.
There was no separate casting director for the child actor roles; the assistant director held open auditions for newcomers, and the cast was selected by anonymous voting among the production staff.
Episode 12 hit a 12.3% rating, surpassing 'Woman of Dignity' to become JTBC's highest-rated drama at the time, and episode 18 later reached 22.316%, breaking the record for non-terrestrial Korean channels previously held by 'Goblin' (20.5%).
The show became hugely popular in China despite the Hallyu ban, airing there unofficially under the title 'Sky Castle' (天空之城); the hashtag was searched nearly 400 million times on Weibo, and state media outlet Global Times ran a front-page story about its online popularity.
Many viewers found the finale's 'good triumphs, evil repents' ending unsatisfying, and some even posted a petition on the Blue House's public petition site demanding that episode 20 be reshot.
The finale's original broadcast date of January 26 was pushed back to February 1 because a live broadcast of the South Korea vs. Qatar AFC Asian Cup quarterfinal match was scheduled for January 25.
South Korea's Ministry of the Interior and Safety released year-end tax settlement promotional material that parodied lines from the drama.
After episode 14 aired, netizens' fan theories about the following episode's plot turned out to be accurate, sparking rumors of a leak; producers stated it was coincidence, but on January 16 it was confirmed that scripts for episodes 17 and 18 had genuinely been leaked online, prompting a police investigation.
The OST track 'We All Lie,' performed by a singer known as Ha-jin, became a viral sensation on YouTube and Melon, though information about the singer remained scarce despite being credited to Warner Music Korea.
The production faced plagiarism accusations that 'We All Lie' copied American singer Bea Miller's song 'To the Grave' featuring Mike Stud, but music director Kim Tae-sung and JTBC denied the claims, stating the melodies and harmonies were entirely different.
A scene depicting a patient threatening a doctor with a knife over a botched operation drew protest from the Korean Medical Association after a real-life murder of a doctor occurred, with the association arguing the scene risked inciting imitation violence.
Most filming took place at a membership resort in Yongin, Gyeonggi Province, and the cast's first script reading was held in August 2018 at the JTBC building in Sangam-dong, Seoul.
The show's title, 'SKY,' references the acronym commonly used in South Korea for its three most prestigious universities: Seoul National University, Korea University, and Yonsei University.
The series inspired international remakes, including an American version tentatively titled 'TriBeCa' for NBC, a Japanese remake also titled 'Sky Castle' that aired on TV Asahi in 2024, and a Thai remake titled 'Sky Castle Thailand.'
