Fate franchise fans get hyped! It was revealed in the official Prisma Illya anime website on Saturday that the upcoming anime film titled Gekijōban Fate/kaleid liner Prisma Illya: Yukishita no Chikai (Movie Version Fate/kaleid liner Prisma ☆ Illya: Oath Under the Snow) is slated to premiere this Summer in Japan. The promotional video also debuted on Saturday at the Kadokawa booth in the AnimeJapan 2017 event.
Seiyuus Mai Kadowaki and Noriaki Sugiyama (voice actresses of Illyasviel von Einzbern and Shiro Emiya respectively) were present as tickets for the film were also on sale in the said event. Those who got their tickets early in February received a limited edition clear file along with their purchase (see above image).
Aside from this visual, a first teaser visual was also released by the staff in September (see below image).
More information can be found in and Animate Times.