A New Galaxy Express 999 Anime Film Is in Production at Toei Animation
Leijisha says Rintaro is attached for story concept, with no title, director, cast, or release window announced yet.

What was announced
A new theatrical Galaxy Express 999 animated film is in production. Leijisha, the company that manages the works of Leiji Matsumoto, posted the announcement to its official site on July 25, confirming that the project has been greenlit and that animation production sits with Toei Animation, which marks its 70th anniversary this year.
The one credit attached so far is Rintaro, listed on story concept. Leijisha's notice describes his representative works as the 1979 Galaxy Express 999 film and Metropolis (2001), but it does not name him as director of the new project.
Beyond that, the announcement is deliberately thin. There is no subtitle or working title past Galaxy Express 999 itself, no director, no voice cast, and no release date or window. Leijisha's post confirms production and nothing more, so anything about scope, story, or timing is unconfirmed for now.
What Leijisha said
Makiko Matsumoto, Leijisha's representative director and Leiji Matsumoto's eldest daughter, framed the film as the fulfilment of a goal her late father held for years. In her comment she notes that roughly half a century has passed since the theatrical Galaxy Express 999 opened, and says Toei Animation gave the company the opportunity to announce a new work that had been Matsumoto's long held wish.
That framing matters, because it positions the project as a continuation of the film lineage rather than a remake of the television series. Leijisha has not said which part of the story the new film draws on.
Background: the 999 on screen
The 1979 Galaxy Express 999 film opened on August 4, 1979. It follows Tetsuro Hoshino, an orphaned boy in a future where immortality can be bought in the form of a mechanized body. He stows away aboard the space train of the title hoping to obtain one and avenge his mother's death, and en route he meets , a woman who is the image of the mother he lost.
