Mamoru Hosoda completed all 500 pages of storyboards for the film at Denny's, working in hugely long 12 and 16-hour shifts.
Warner Brothers originally considered localizing the film themselves before licensing it off to FUNimation Entertainment.
The name of the rogue AI, Love Machine, is a pun. "Ai", in Japanese, means love.
The grandmother's birthday, August 1st, is a clear reference to Odaiba Day, a holiday celebrated within the Digimon fandom that is recognized and acknowledged by many Digimon media producers. The director to Summer Wars, Mamoru Hosada, has a history with working on and directing Digimon media, most notably a movie he directed, "Digimon Adventure: Our War Game" (localized theatrically outside of Japan as "Digimon: The Movie") which shares a very similar art style, themes, and plot points to Summer Wars.