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Pop-up message

Launch Game with custom arguments

Fallout 4 is attempting to launch with optional parameters shown below:

-len

If you did not request this launch or do not understand these options, select Cancel.

This is the exact pop-up and what I see when I try to boot up Fallout 4. Why does it say it needs to open with "optional parameters"?

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There's a Steam Community Discussion in relation to this. It also links to a Troubleshooting Guide on Steam. Users report a variety of different fixes, and a comment in the first thread sums it up well (after they found another different fix):

Given the variety of solutions here ..., you may just as well pray to cthulhu under a full moon while aligning your chakras.

PCGamingWiki also has fixes listed, and of course much more, but not this yet.

Some fixed this by just not running the game as admin. Running Steam as admin is not recommended, i.e. how a Steam bug once deleted all of a users drive. Games should be run as admin without Steam doing so.


Most fixes seem to imply this is a launcher issue, and Steam user Cheshirm found evidence of that in logs from Steam:

in ...\steam\logs\content_log.txt I found ... the game launcher [starts] the game with -len.

[2024-05-22 12:59:46] AppID 377160 adding PID 1428 as a tracked process ""D:\SteamLibrary\steamapps\common\Fallout 4\Fallout4.exe" -len"

Steam user Laurens details how to use a launch arg to skip the launcher in another Steam discussion.

Right-click Fallout 4 in Steam and go to properties. Click "Set Launch Options" and type the following:

"C:\Games\steamapps\common\Fallout 4\Fallout4.exe" %command% -NoLauncher

The location path should direct to your own Fallout 4 folder of course.

Similar can be accomplished by swapping the file names of Fallout4Launcher.exe and Fallout4.exe according to a quoted but deleted answer/comment earlier in the above Steam discussion. This will need to be fixed again after verifying the game cache (if ever), and will cause it to "fail" and download at least these two files again.

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