Shinobumonogatari (忍物語) is the upcoming eighteenth part of the Monogatari Series. It will be the twenty-third book and the first book of Monster Season. It will be released sometime in 2017.
The teaser in the back of Musubimonogatari reads:
"What of the one who named the legendary oddity(ies) Araragi Koyomi confronts?" and "Do not overlook the blade-point, which has endured a long age of submission and gleams."