After Act II

In this chapterThe Survivor must choose between four factions: the Institute, the Brotherhood of Steel, the Railroad and the Minutemen.

With the Institute revealed, the Commonwealth's factions seek the Survivor's help. Maxson's Brotherhood wants to destroy the Institute and eliminate synths. Desdemona's Railroad wants to free synths and sabotage the Institute. Garvey's Minutemen offer a flexible alliance. The Survivor can work with one faction, and eventually must decide which one will win. Each has different quests and companions, and each leads to a different final mission.

The final act forces the Sole Survivor to pick a faction. The Brotherhood of Steel is a militaristic and paranoid group, but it has a coherent belief: technology is dangerous, and the Institute is the worst example. Maxson is a young, determined leader who is willing to use force to protect the Commonwealth.

The Railroad is a clandestine group that treats synths as people. Its members are idealists, but also reckless, and their methods of sabotage and disguise are risky. They offer the most humane choice, but at a cost of violence and secrecy.

The Minutemen are the most hopeful faction. They believe in community and mutual help, and their ending is the most open. The Survivor can use them to balance the others or to carry out a final plan of their own. The Brotherhood sees synths as a threat. The Railroad sees them as people. The Minutemen are the middle path, rebuilding the Commonwealth.

The factions' goals cannot all be met.

In this chapterIn the Brotherhood ending, Maxson and the Prydwen attack the Institute, destroying it and killing Shaun.

The endings are determined by the faction the Survivor chooses. The Brotherhood and the Minutemen destroy the Institute in an assault; the Railroad frees the synths; and the Institute path sees the Survivor take leadership and destroy the other factions.

Each choice has consequences for Shaun, the synths and the Commonwealth. The Survivor can sometimes persuade Shaun to hand over the Institute, or must fight him, and the final result depends on faction relations. Each ending resolves the Institute differently, and the consequences are shown in the epilogue.

The four endings are designed to show different views on technology and humanity. Brotherhood: control by force. Railroad: freedom through secrecy. Minutemen: community and consent. Institute: progress with a cost.

Shaun's fate is the emotional core. In several endings he dies or is left behind, and the Survivor must accept that the child they lost never came back. In the Institute ending, he gives them the leadership, and the Survivor takes the burden.

The Commonwealth after the game is shaped by the choice. The Brotherhood leaves a military presence, the Railroad leaves free synths, the Minutemen leave a network of settlements and the Institute leaves a new power. Every ending has a cost: the Institute's destruction removes its science, but keeping it means keeping its secrets. The Sole Survivor's relationship with Shaun is part of the ending in every route.