From what I can understand from the Store page you can only multiplayer with other GoG users, which is fine I have no interest in playing against a total Stranger on Steam. But nor do I want to play against a stranger on GoG either.

Does Dying Light support locally hosted games? or am required to connect to a 3rd party server to play with the person sitting 2 foot away.

Does LAN work between the Steam and GOG versions?

Shouldn't it? LAN is not dependent on clients, after all.

You would think so. xD
Sorry for asking a stupid question. xD

It's not stupid. If the game versions are even just slightly different LAN might not work.

Is LAN considered "local multiplayer" though? I thought the term was primarily used for when only one machine is used and both/all players use the same screen (split or not).

Dying Light uses some Steamworks features, so I guess it doesn't work without fiddling with cracks. Local Area Network. ¯\_(ツ)_/¯

Can't get simpler than that. xD

On second thought, it seems like it wasn't stupid after all. :/
https://www.gog.com/forum/dying_light/multiplayer_only_available_for_gog_galaxy_users/post8

Sorry for assumptions. Should lern2research better next time.