Do all mods work with Game Pass?
No. Unfortunately, mods that rely on the popular script extenders (SKSE, F4SE, etc) will not currently work with Game Pass. In a conversation with Ian Patterson of the Silverlock team, he said they are experimenting with a few possible solutions at the moment. Sadly, despite their efforts, there are still some hurdles to overcome due to the complications introduced in these new versions, but they haven't given up yet so there's always hope. This may prevent visual presets such as ENBs and ReShades from working correctly, too.
Mods that offer replacements to files from the vanilla game such as video replacers may also be unsupported. This is related to the Xbox app preventing edits to these files. However, in testing, this seems to be a somewhat intermittent problem so your mileage may vary.
Don't worry though, there are still plenty of mods that will work just fine!
How do I install mods on the Game Pass version?
Out of the box, the ability to install mods to the game is disabled. In this state, none of the game files can be modified by your user account. You will need to enable modding in the Xbox app by clicking the "Enable Mods" button shown below.

Once enabled, you will be able to make changes to the files in the game-specific folder found at C:\Program Files\ModifiableWindowsApps\.
You'll be pleased to know our Vortex devs are already hard at work on updating the extensions for Skyrim SE, Fallout 4, Oblivion and Morrowind to include support for the Game Pass versions. Keep an eye out for an update!
What about modding tools like xEdit?
Any tools you are used to using to mod your game will likely not support Game Pass without being updated first. Please make sure you check the mod page for the tool you are trying to use to see if the author has added any information about Game Pass before asking them.
As a mod author, do I need to update my mods?
There shouldn't be any need for mods to be updated for this version of the game. However, if your mod does rely on script extender functions and you want to support the Game Pass release, you could consider making these functions an optional requirement. I've personally already done this in Icecreamassassin's Legacy of the Dragonborn back when SKSE was not yet available for Skyrim Special Edition. I'd be happy to offer advice to anyone who is interested.
What else is different?
Based on a combination of our own research and some information from the team behind Wryebash, we've compiled a list of notable differences in important file paths for each of the Game Pass versions. All of these games must be started through the game launcher via the Xbox app and it may not be possible for mod managers to detect the game from a "cold start" of the system due to the game files needing to be "mounted" for it to be detectable. The fix for this is just to open and close the game once before managing mods.
Skyrim Special Edition
Game Pass Publisher ID: 3275kfvn8vcwc
Game Pass ID: BethesdaSoftworks.SkyrimSE-PC
Mod Install Location: C:\Program Files\ModifiableWindowsApps\Skyrim Special Edition (PC)
INI/Saves Location: C:\Users\{USER}\Documents\My Games\Skyrim Special Edition MS
Plugins.txt Location: %localappdata%\Packages\BethesdaSoftworks.SkyrimSE-PC_3275kfvn8vcwc\LocalCache\Local\Skyrim Special Edition MS\Plugins.txt
Fallout 4
Game Pass Publisher ID: 3275kfvn8vcwc
Game Pass ID: BethesdaSoftworks.Fallout4-PC
Mod Install Location: C:\Program Files\ModifiableWindowsApps\Fallout 4 (PC)
INI/Saves Location: C:\Users\{USER}\Documents\My Games\Fallout4 MS
Plugins.txt Location: %localappdata%\Packages\BethesdaSoftworks.Fallout4-PC_3275kfvn8vcwc\LocalCache\Local\Fallout4 MS\Plugins.txt
Note: The Fallout 4 version on Game Pass does not include any of the DLCs, they can be purchased separately.
Oblivion
Game Pass Publisher ID: 3275kfvn8vcwc
Game Pass ID: BethesdaSoftworks.TESOblivion-PC
Mod Install Location: C:\Program Files\ModifiableWindowsApps\Oblivion GOTY (PC)
INI/Saves Location: C:\Users\{USER}\Documents\My Games\Oblivion
Plugins.txt Location: %localappdata%\Packages\BethesdaSoftworks.TESOblivion-PC_3275kfvn8vcwc\LocalCache\Local\Oblivion
Note: Oblivion installs several different language versions of the game in separate folders. The mod installation location will vary depending on which version you are trying to play.
Morrowind
Game Pass Publisher ID: 3275kfvn8vcwc
Game Pass ID: BethesdaSoftworks.TESMorrowind-PC
Mod Install Location: C:\Program Files\ModifiableWindowsApps\Morrowind GOTY (PC)
INI/Saves Location: C:\Program Files\ModifiableWindowsApps\Morrowind GOTY (PC)
Note: Morrowind installs several different language versions of the game in separate folders. The INI and mod installation locations will vary depending on which version you are trying to play.
Repairing your installation
In the event that you delete or damage some of the core vanilla game files, you can actually reverify the game files similar to how it works with Steam. This option isn't part of the Xbox app itself but can be found in your Windows settings. Open your Windows settings, go to Apps, then find the game in the list of installed apps. Click on the game entry and it will allow you to select "Advanced options" where you can repair or reset your game installation.

Did we miss anything? What do you think about the Bethesda games being available on Game Pass? Let us know in the comments below.