Fallout 4 Main Quest Guide: All Endings and Faction Choices Explained

This article is based on information as of June 4, 2026. Fallout 4 does not have a season system. The closest concept is the “next-gen update” released on April 25, 2024, which is the latest major update. This update primarily focuses on performance improvements for PlayStation 5 and Xbox Series X|S, widescreen support, multiple bug fixes, and the addition of free Creation Club content, including new quests such as “Enclave Remnants.” It does not directly change the core story or ending branching conditions of the main quest.

As the sole survivor of Vault 111, awakened from cryogenic sleep, you step into the unknown post-apocalyptic world of The Commonwealth to retrieve your son Shaun, who was snatched away before your eyes. However, this journey eventually transforms into an epic tale that determines the future of this world. Which faction will you align with, and what ending will you achieve? This article provides a complete guide to Fallout 4's main quest, thoroughly explaining the intricately intertwined faction relationships and the irreversible turning points of fate.

Main Quest Overview

Act 1-2: The Road to Finding Shaun

From the early to mid-stages of the story, the main focus is on linear quests following your son Shaun's whereabouts. You will encounter the major factions of The Commonwealth while pursuing important milestones.

1. Out of Time: The beginning of the story. Reunite with Codsworth in your hometown of Sanctuary Hills and meet the Minutemen in Concord.
2. Unlikely Valentine: Find detective Nick Valentine in Diamond City and, by rescuing him, gain clues about Shaun's kidnapper.
3. Reunions: With Nick's help, track down the mercenary “Kellogg,” the perpetrator of Shaun's kidnapping, at Fort Hagen. Here, the existence of the Institute becomes clear for the first time.
   • Tips: In Fort Hagen's command center, you'll find a valuable “Energy Weapons Bobblehead” and a “RobCo Fun” magazine. Don't forget to collect them before the battle with Kellogg.
4. Dangerous Minds: Extract memories from Kellogg's brain in Goodneighbor to find a way to infiltrate the Institute. During this process, it is revealed that you must cross The Glowing Sea.
5. The Molecular Level: The climax of the mid-story. You will build a “Signal Interceptor” to teleport to the Institute. Building this device requires advanced technology, and you will choose which faction to seek cooperation from.
   • Minutemen: With Sturges's cooperation, it can be built most simply.
   • B.O.S.: Consult Proctor Ingram on the Prydwen. They offer extensive technical support and opportunities to acquire powerful equipment.
   • Railroad: Enlist the help of Tom the Tinker. This is a good fit if you are skilled in stealth and hacking.
   Regardless of which faction you seek cooperation from, you will not be hostile with other factions at this point. However, this choice will begin to affect your relationships with the factions later on.

Four Factions Determining the Future of The Commonwealth

Once you reach the Institute, the story enters Act 3, and serious faction choices begin. Understand their respective ideologies and decide who you will walk with.

Minutemen

A volunteer militia dedicated to protecting the common citizens of The Commonwealth. They are an “organization of the people, by the people,” and you, as General, aim to rebuild them. They take a neutral stance, not leaning towards any particular ideology, and can strive for coexistence with other factions.

Brotherhood of Steel (B.O.S.)

A massive military organization whose mission is to secure and manage pre-war advanced technology and eliminate threats to humanity (such as synths, Super Mutants, and other mutants / creatures). They possess powerful Power Armor and Vertibirds, but their ideology also has exclusive and extreme aspects.

Railroad

An underground organization dedicated to protecting synths who have escaped from the Institute and granting them freedom. They excel in intelligence gathering and stealth operations and are in direct opposition to the B.O.S., who do not recognize synths as human, and the Institute, who view synths as property.

Institute

A mysterious group of scientists with vast underground facilities. They possess advanced technology and aim to redefine The Commonwealth by manufacturing synths. They consider the people on the surface to be a degraded existence and believe themselves to be the future of humanity.

[Most Important] Irreversible Choices: "Point of No Return"

As you progress through the main quest, there will come a moment when completing certain quests will permanently make you hostile with other factions, making it impossible to go back. If you wish to see all endings or maintain relationships with specific factions, it is strongly recommended that you save before the following quests.

Branching Point 1: Institute vs. B.O.S. (Quest "Mass Fusion")

When you start the Institute quest "Mass Fusion," a moment of decision arrives. The objective of this quest is to retrieve the beryllium agitator from the Mass Fusion building.

1. Speak with Allie Filmore inside the Institute and agree to use the molecular relay.
2. The moment you use the molecular relay, you will become permanently hostile with the B.O.S. A warning transmission will come in from the B.O.S., and the quest "Spoils of War" will fail.
• To proceed with the B.O.S. route: Before using the molecular relay, report the Institute's plan to Proctor Ingram on the Prydwen. This will cause the Institute quest "Mass Fusion" to fail, initiate the B.O.S. quest "Spoils of War," and permanently make you hostile with the Institute.

Branching Point 2: B.O.S. vs. Railroad (Quest "Tactical Thinking")

After progressing through the B.O.S. questline and making a critical decision regarding Paladin Danse in "Blind Betrayal," caution is required.

1. Speak to Captain Kells on the bridge of the Prydwen.
2. Speaking with him will automatically initiate the quest "Tactical Thinking."
• Moment of Hostility: The moment this quest begins, you will become permanently hostile with the Railroad. Members of Railroad Headquarters will become hostile NPCs, and all related quests will become uncompletable. If you wish to maintain your relationship with the Railroad, absolutely do not speak to Captain Kells.

Branching Point 3: Institute vs. Railroad (Quest "End of the Line")

As you progress through the Institute route, you will be ordered to annihilate the Railroad.

1. Receive the quest "End of the Line" from Father.
2. You will be ordered to eliminate the leaders at Railroad Headquarters.
• Moment of Hostility: The moment you accept this quest and attack any Railroad members, you will become permanently hostile with them.

Explanation of All 4 Ending Routes

The story branches into four different endings depending on which faction's questline you ultimately complete.

Minutemen Route: The Last Bastion

This route serves as a "fallback" option, allowing you to complete the game even if you are hostile with all other major factions. The ultimate goal is to destroy the Institute. You will proceed through the quest "Defend the Castle" to the final quest "The Nuclear Option (Minutemen)." Depending on how you play this route, it is possible to achieve the most peaceful outcome, allowing the B.O.S. and Railroad to coexist without becoming hostile.

B.O.S. Route: Steel Reign

This route purifies The Commonwealth with the overwhelming military might of the B.O.S. You will reactivate the colossal weapon Liberty Prime and physically destroy the Institute. The final quests are "Ad Victoriam" and "The Nuclear Option (Brotherhood)." In this process, the Railroad will also be annihilated, ushering in an era of B.O.S. control and management of technology in The Commonwealth.

Railroad Route: Dawn of Liberty

This route achieves the liberation of synths through intelligence and strategy. You will infiltrate the Institute and destroy the Prydwen, the B.O.S.'s ace in the hole. Ultimately, the Institute will also collapse from within. The final quests are "Rockets' Red Glare" and "The Nuclear Option (Railroad)." While freedom is brought to synths, the power structure of The Commonwealth will be significantly shaken.

Institute Route: Redefining Humanity

This route sees you become the new leader of the Institute, guiding the organization's future. You will eliminate the surface threats of the B.O.S. and the Railroad and begin the management of humanity based on the Institute's ideology. Upon completing the final quests "Airship Down" and "Nuclear Family," the story quietly concludes not on the surface, but within the underground Institute.

Summary

Fallout 4's main quest is more than just a story about finding your son. It's also a journey that asks the player what ideals people uphold to live and build a future in a devastated world. The Minutemen, B.O.S., Railroad, and Institute each have their own sense of justice. Using the "Points of No Return" introduced in this article as a guide, be sure to create a save before making critical decisions, and explore all possibilities. Your choices will determine the very future of The Commonwealth.