Zoku Owarimonogatari serves as the “final” volume for the Monogatari series, and is also part of its “Final Season”. Now, the anime’s official website has unveiled its new PV, as well as its new key visual.
— 西尾維新アニメプロジェクト (@nisioisin_anime) December 27, 2017
However, while the staff have already revealed the new anime’s PV and visual, they still haven’t revealed its format. As of writing, it’s still unclear whether Zoku Owarimonogatari will be a TV anime, OVA, or film. It looks like we would have to wait a bit for the staff to make more announcements.
As for the source itself, NisiOisin released the light novel back in 2014 to serve as the “ending” for the franchise. However, he also released several other Monogatari volumes after that. This includes four “Off-Season” light novels, as well as the “Monster Season”. But then again, author NisiOisin has gained quite the reputation for word play and trolling. His latest Monogatari work, Shinobumonogatari, got its release back in July.