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Z4K-97B 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. Z4K-97B, along with A-2018 and XPN-20A, will serve as the game's final boss during all endings other than the Institute ending.

Interactions with the player characterEdit

Interactions overviewEdit

General Services Quests
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Companion: noIcon cross
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The Nuclear Option


Apparel Weapon Other items On death
Synth uniform Reactor terminal password


  • Z4K-97B wears a special variant of the synth armor which is jet black in color and can be shot off by focus fire and explosives, much like power armor.
    • XPN-20A and A-2018 wear identical sets of this unusual armor.
    • Said armor cannot be obtained via looting, pacify trading/armor swap, companion inspecting, etc.
  • Z4K-97B will always spawn as a Legendary enemy.


Z4K-97B appears only in Fallout 4.

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