Is ONE PIECE episode 809 filler?
Canon No, episode 809 of ONE PIECE is canon.
#809
A Storm of Revenge! An Enraged Army Comes to Attack!
復讐の嵐 怒りの軍団襲来!
Aired 15 Oct 2017
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.