Sailor Moon Crystal (which goes by Pretty Guardian Sailor Moon Crystal in Japan) is getting a fourth season after three seasons and 39 episodes. However, the Toei Animation series' fourth season won't be another 13 episode installment- instead, it will be released as a 2-part film in Japanese theaters. The film will adapt the Dead Moon arc from Naoko Takeuchi's original manga. [Fun fact: Takeuchi is married to Yu Yu Hakashu and Hunter x Hunter mangaka Yoshihiro Togashi.]
Before being confirmed on the show's official website, the announcement was made earlier today in Japan at the "25th Anniversary Usagi Birthday Event" in Tokyo.
Crunchyroll and Hulu streamed the firs three seasons of Sailor Moon Crystal as they aired in Japan.
From a technical standpoint, each season of Sailor Moon Crystal was 13 episodes, with each episode consisting of about 24 minutes. Take out opening and closing theme songs and you're likely looking at about 20 minutes of actual new footage. That means each season consisted of about 260 minutes of new material. That means to have an equal amount of new footage for the two films making up season 4, each film would need to be 130 minutes or 1 hr and 10 minutes.