The project was first mentioned in September 2016 in an interview with Hiroyuki Yamaga and Yoshiyuki Sadamoto. At that time, Yamaga was writing the script for the series prior to writing the script for Uru in Blue. His intent at the time was to connect Gubuster and Diebuster together with the new story, and that characters from them might briefly appear, but that overall the story would be completely different and the most clear link between the three would be in "the SF aspect".
The project was reconfirmed in 2018, now in production under the branch of Gainax known as Gaina. No new information was revealed about it, but Uru In Blue was given a release date of 2022, which may mean that Gunbuster 3 could come later than that.