From GameWatcher: “One of the wilder instances of fun Fallout lore are the so-called Zetas, or the aliens we’ve all come across while playing Fallout video games. While they’ve not yet made an appearance in Fallout 76, we do know for a fact that their trademark “firearm” – the Alien Blaster – definitely will.”
Source: N4G PC Alien Blaster Can be Found in Fallout 76 – Where Are The Aliens?