XPN-20A

XPN-20A is a synth living in the Commonwealth in 2287. He is a hostile synth encountered in the Institute's reactor room during the quest The Nuclear Option with any faction. XPN-20A, along with A-2018 and Z4K-97B, will serve as the game's final boss during all endings other than the Institute ending.

Appearances
XPN-20A appears only in Fallout 4.

Bugs
Unlike Z4K-97B and A-2018, XPN-20A does not spawn in the reactor room, but next to the elevator at the center of the main floor, before going into the Advanced Systems wing. Thus making the last fight a bit easier.