I greatly appreciate the level of detail in GOG's releases, to the extent they go ahead and put those creation kits right inside Gamebryo engine games so we don't have to. There's one slight oversight though. Morrowind, Oblivion, and New Vegas all have the latest creation kits but Fallout 3 has an outdated version by default.

https://geck.bethsoft.com/index.php?title=Main_Page

Bethesda's page includes a link to this updater which raises the version automatically to 1.5
https://cdn.bethsoft.com/fallout/3/geck/Fallout3_GECK_1.5_Update.exe

I provide these links to help others and request GOG update their installer to use these updated files in the Fallout 3 folder rather than the older version.