Setting up Online Subsystem Steam in Unreal
2 min read
By Eduardo Orellana ·
To set up Online Subsystem Steam in Unreal: load the OnlineSubsystemSteam module, then in DefaultEngine.ini set [OnlineSubsystem] DefaultPlatformService=Steam, [OnlineSubsystemSteam] bEnabled=true and SteamDevAppId=480 for testing, and point GameNetDriver at OnlineSubsystemSteam.SteamNetDriver with the IP driver as fallback. If you use Sessions, uncomment bInitServerOnClient=true, or Create and Join Session will not work. Run with the Steam client open.
The configuration, from Epic's documentation
Add the module to your game's build file (DynamicallyLoadedModuleNames.Add("OnlineSubsystemSteam")) or enable the plugin, then add to DefaultEngine.ini:
[/Script/Engine.GameEngine]
+NetDriverDefinitions=(DefName="GameNetDriver",DriverClassName="OnlineSubsystemSteam.SteamNetDriver",DriverClassNameFallback="OnlineSubsystemUtils.IpNetDriver")
[OnlineSubsystem]
DefaultPlatformService=Steam
[OnlineSubsystemSteam]
bEnabled=true
SteamDevAppId=480
; If using Sessions
; bInitServerOnClient=true
[/Script/OnlineSubsystemSteam.SteamNetDriver]
NetConnectionClassName="OnlineSubsystemSteam.SteamNetConnection"What each part does
- DefaultPlatformService=Steam makes Steam the online subsystem.
- SteamDevAppId=480 uses Valve's shared test app; replace it with your own App ID before shipping.
- The net driver lines carry game traffic over Steam's networking, falling back to plain IP.
- bInitServerOnClient=true is needed for Sessions; lobbies work without it.
- bUseSteamNetworking=false (4.22 and later) turns Steam's socket networking off if you only want the other features.
Testing
- The Steam client must be running and signed in.
- Unreal writes steam_appid.txt beside the executable and removes it on a clean exit; never upload it.
- Test multiplayer between two machines on two Steam accounts, not two instances on one.
- Shipping builds verify ownership, so test those from Steam with your real App ID.
Where Flockbay fits
Flockbay builds games on Godot, where GodotSteam does this job. Its publishing tools work for an Unreal game too, free in beta until 1 December 2026.