Revealed at Tennocon 2018.
Figured I should clarify since some people are posting about this gun being a dual wielding weapon - the only reason it isn't shown like that is because the concept artists only have a few basic 'grips' readily available to us to use: pistol pose and rifle pose. These are purely meant to test the grip to make sure we've designed a gun which can be held by a character. This is also why you don't see the concept artists posting images of tenno holding melee weapons and such.