The novel series’ “final season” ended with Zoku Owarimonogatari in September 2015, but it featured a teaser for “Monogatari Series, Next Season Tsugimonogatari.”
Amazon is listing Shinobumonogatari, the next novel in NisiOisin’s Monogatari Series of novels, with a July 15 release date.
Vertical published the earlier Kizumonogatari novel in December 2015, and began publishing the original Mongatari Series novels beginning December 2016 with the Bakemonogatari novels.
The most recently announced anime adaptation tackles the third Owarimonogatari novel.