I was surprised seeing Serious Sam 4 getting a release on GOG, as the later ones heavily relied on Steamworks for Multiplayer. But with it coming to GOG and supporting Coop here, I wonder if there will be crossplay between GOG and Steam versions (and maybe Stadia too), as I prefably buy games on GOG, but not all my friends do.

Star Wars Battlefront II from 2005 has GOG Multiplayer on both, GOG and Steam. So, maybe SS4 could work the same?

I'm not sure if I'll buy SS4 on GOG, because I have all other SS games on Steam. But maybe I wlll end up on GOG. Did the same with Witcher 3, where I bought Witcher 1 & 2 on Steam before.

I hope so. I also hope the map editor will be available for the GoG version. It'd be like a dream come true. Never thought I'd see any modern SS games here, let alone the newest one on launch day.

Does someone have any new info on this topic?

Has anyone purchased yet.
Does this have direct IP for co-op
because 'Seriously' if it doesn't the value prop for this game is at 10 bucks max.
Not having multiplayer for an FPS in the modern age is basically heresy; and not making it available because... PIRATES!!! is anti-consumer and i won't support a company that does.

Someone asked in the Croteam subreddit, and got an answer from a dev:

Hey guys. Unfortunately, there's no cross play support at the moment. On Steam we are using their matchmaking system, and same goes for GOG. We don't have our own master servers.

https://www.reddit.com/r/Croteam/comments/iyza0q/serious_sam_4_gog_and_steam_crossplay/g6gw2rk/

I have all the SS games on Steam and am considering getting 4 here. I'm a little cautious after reading the reviews

Anyone who has a friend with the Steam version, try this method to connect and see if it works:

"
You can also do it from inside the game with these console commands:
gam_strConnectToIP = "ipaddress:port"
gam_esgaStartAs = 2
gamStart()

replace ipaddress:port with the server's ip address and port. You have to write the port even if the server uses the default one (in that case, it is 27015).
Example for a server with ip address 111.22.3.174, listening on port 33173
gam_strConnectToIP = "111.22.3.174:33173"

( what gam_strConnectToIP is for should be self-explanatory. gam_esgaStartAs tells the game to start a game session where the game is a client on a multiplayer session. gamStart() starts a game session with previously defined settings. )
"

Information taken from a Serious Sam 3 Steam thread, but the console commands in Serious Sam 4 are almost identical, I believe.