The Arcanist class is yet to be implemented into the game. They have models in the game's files, but as of now, are considered unfinished and thus unplayable in their current state. Although the Arcanists or at least people called Arcanists are sometimes mentioned within the game's lore.
According to writing on a wall a man named Ioter was an Arcanist who gathered his courage before going to the Necropolis on a pilgrimage.