Fallout London requires Fallout 4. Unfortunately, I do not have the game on GOG. The steam version has what's called the "next gen update", which means it's not compatible with Fallout London, you'll have to download an older version (1.10.163.0) from steam. You can do this manually using steam console commands, or you can use a tool specifically designed for this.
You need to own the following content:
- Fallout 4
- Automatron
- Far Harbor
- Nuka World
- Wasteland Workshop
- Contraptions Workshop
- Vault-Tec Workshop
Easy Method:
Download the Fallout London Downgrader from
Nexusmods, and follow it's instructions (requires providing your steam credentials, though).
Manual Method:
1. Access
in a browser or via the windows run dialog (Win + R)
2. Download the following depots:
Part A:
Code:
download_depot 377160 377161 7497069378349273908
Part B:
Code:
download_depot 377160 377163 5819088023757897745
Executable
Code:
download_depot 377160 377162 5847529232406005096
English Language
Code:
download_depot 377160 377164 2178106366609958945
HD Textures
Code:
download_depot 377160 540810 1558929737289295473
Automatron
Code:
download_depot 377160 435870 1691678129192680960
Automatron English Language Pack
Code:
download_depot 377160 435871 5106118861901111234
Wasteland Workshop
Code:
download_depot 377160 435880 1255562923187931216
Far Harbor
Code:
download_depot 377160 435881 1207717296920736193
Far Harbor English Language Pack
Code:
download_depot 377160 435882 8482181819175811242
Contraptions Workshop
Code:
download_depot 377160 480630 5527412439359349504
Vault-Tec Workshop use
Code:
download_depot 377160 480631 6588493486198824788
Vault-Tec Workshop English Language Pack
Code:
download_depot 377160 393885 5000262035721758737
Nuka World
Code:
download_depot 377160 490650 4873048792354485093
Nuka World English Language Pack
Code:
download_depot 377160 393895 7677765994120765493
Content will be downloaded to "C:\Program Files (x86)\Steam\steamapps\content\app_377160" into separate folders, you'll need to merge the contents of these folders into a single folder ("C:\Program Files (x86)\Steam\steamapps\common\Fallout 4")
3. Disable automatic updates by marking the file "C:\Program Files (x86)\Steam\steamapps\appmanifest_377160” as read only
4. Install Fallout London
I can't personally test it, because I only own the Base game of Fallout 4, not the required DLC/GOTY content.