The season (1 cour) will include the first two books.
That includes Ougi Formula (seems to be airing entirely on October 3rd as a special), Sodachi Riddle, Sodachi Lost and Shinobu Mail.
Scripts for the last book's adaptation are complete but they're looking for a better timing to present those stories.
Anime adaptation of Koyomimonogatari is in planning stages.
Source.
Kizu never.