If I buy the Gog version, can I play with Steam version players?

The devs communicated on their Discord that that would not be possible, at least initially.

I know it was asked about Steam, which isn't available. But under the system requirements, it does list the following:

Please note: GOG GALAXY is required to access online features for Stronghold: Warlords.
Multiplayer is available only between GOG users.

I do hope the Devs and GOG work this out and enable crossplay. I hate being treated like a 2nd class customer, and it may be in GoG's interest to give the devs as much support needed to get this working, since crossplay removes a barrier to buying it on GoG. It is hard to choose between worse multiplayer and drm free.

It's not DRM Free if it's tied to Galaxy client bro ... so all that DRM FREE is bullshit so far, at least if it had a LAN mode it would have been DRM FREE but it doesn't !

I agree, but GoG is more reliable in terms of, even if they ban one of us for thinking naughty politically incorrect thoughts du jour, I have the offline installer, and can still enjoy the game. Granted, lan multiplayer would be ideal, but for steam I heard of people losing their entire catalogue for not towing the current political line.

That said, I hope for a lan multiplayer mode. Its not that this game is going for ranked multiplayer or anything, too niche for that, and lan multiplayer allows friends to play each other easily.

What? No wonder i dont find any MP Games... That sucks. Refund is coming....