Fallout Worlds

Fallout Worlds and Custom Worlds are game modes Although the rotating Fallout Worlds is accessible to all players, the customizable Custom Worlds feature is only accessible to Fallout 1st subscribers and their friends.

Overview
Fallout Worlds brings two game modes to the main menu screen:
 * Public Worlds: monthly rotating public worlds with settings hand picked by the developers; available to all players
 * Custom Worlds: a private world with settings customized by the player; available to Fallout 1st subscribers and their friends

Any progress made on Public or Custom Worlds is not linked to Adventure Mode, instead, it is specific to those worlds. Your Adventure Mode character may be cloned/synced at any time for up to a total of 5 concurrent Fallout World character slots. If a Public World is unavailable for play, the character progress will be lost.
 * Progression

Atom challenges may not be completed while playing on both Public and Custom Worlds, although daily and weekly S.C.O.R.E. challenges can be. Scoreboard rewards and currencies including perk card packs, gold bullion, caps, legendary modules, legendary scrip and atoms can also not be claimed in Public and Custom Worlds.

Public Worlds
Public Worlds mode is offered as an alternative to the normal gameplay, featuring special preset Fallout Worlds designed around a theme. A player may join a Public World at any time, as Fallout 1st is not a requirement to participate in this feature. Public Worlds will be rotated on a monthly basis when available on the live version of the game but will be rotated weekly during their debut on the Public Test Server. Public Worlds are limited to 24 players. 

Custom Worlds
Custom Worlds are the next evolution of Private Worlds, allowing Fallout 1st subscribers to tweak and personalize their Fallout 76 experience. Additionally, friends or teammates of Fallout 1st members may join Custom Worlds, although they cannot configure or host their own settings. Private Worlds are limited to 8 players.

As up to three Custom World loadouts may be stored, they may be personalized with a unique name, description and styled with one of 20 Vault Boy perk images. Several words and characters, however, are blacklisted from use.

Customization options
Custom Worlds may even be created without any configuration settings.
 * Note: Default setting values are bolded.

Behind the scenes

 * Several icons for Fallout Worlds were posted on Jake Raymor's ArtStation.
 * Dweller Must Die is in reference to the Devil May Cry series and its hardest unlockable difficulty Dante Must Die that has appeared in all games. Additionally, both the Dweller and Dante Must Die difficulty modes generally achieve the same effect of difficulty by making enemies tougher/more resistant and do increased damage to the player.