Bessatsu Shonen Magazine, the magazine that publishes the Japanese version of
Attack on Titan, has announced that the spin-off novel
Attack on Titan: Lost Girls —which is actually a compendium of three different stories:
Lost in the Cruel World, about Mikasa;
Wall Sina, Goodbye, about Annie; and
Lost Girls, about both— will be adapted into a manga series, that will start its publication in the next issue of the magazine, to be released on August 9.
Additionally, they have announced that Attack on Titan: Before the Fall will be published again; and that there will be an "important announcement" about the comedic parody Attack on Titan: Junior High, but with no further details revealed yet. Maybe an anime adaptation? We'll have to wait to August to know more about this new expansion of the Attack on Titan universe.
Source: Anime News Network