In the new description for the Lightsaber book coming out in October, there's a blurb about it having details for a 'new, never before seen' type of saber from The High Republic, & also details about the Darksaber.
I know it's a few months away, but it'll probably be the best official reference we get for a while.
I know it's a few months away, but it'll probably be the best official reference we get for a while.