It's been known since late 2017 that they were working on a CG movie, but no details about what it was about until today:
https://www.animenewsnetwork.com/ne...-howl-moving-castle-diana-wynne-jones/.160215
https://www.animenewsnetwork.com/ne...-howl-moving-castle-diana-wynne-jones/.160215
Studio Ghibli announced on Wednesday that it is producing an anime movie adaptation of author Diana Wynne Jones' Earwig and the Witch (Aya to Majo) novel for a television premiere on the NHK General channel this winter. Hayao Miyazaki's son Goro Miyazaki is directing the movie as the studio's first full 3D CG feature, and the elder Miyazaki is credited for the movie's planning and development. Studio Ghibli co-founder Toshio Suzuki is producing.
Jones' Howl's Moving Castle also inspired a 2004 anime film by Hayao Miyazaki, and the film earned an Academy Award nomination for Best Animated Feature.
Jones published the novel in 2011, and Publisher Harper Collins describes the story:
Not every orphan would love living at St. Morwald's Home for Children, but Earwig does. She gets whatever she wants, whenever she wants it, and it's been that way since she was dropped on the orphanage doorstep as a baby. But all that changes the day Bella Yaga and the Mandrake come to St. Morwald's, disguised as foster parents. Earwig is whisked off to their mysterious house full of invisible rooms, potions, and spell books, with magic around every corner. Most children would run in terror from a house like that . . . but not Earwig. Using her own cleverness—with a lot of help from a talking cat—she decides to show the witch who's boss.