Elden Ring Seamless Co-op does not install like a normal Steam feature. You download the mod manually, place it in the game folder, set one shared password, and start the game through ersc_launcher.exe.
Here is the clean current setup for PC and Steam, including Steam Deck, existing saves, and the fixes that solve the common launch and connection errors.
1. Start With the Right Version
The current verified setup is for Elden Ring on PC through Steam. Every player needs a unique Steam copy, and everyone in the group must run the same Elden Ring version and the same Seamless Co-op version.
Use the official Seamless Co-op page on Nexus Mods as the main download source. The research showed Nexus at Seamless Co-op version 1.9.9, while the visible GitHub mirror release showed BETA v1.9.8.
Keep Steam online before you launch the mod. Steam Offline Mode is not the setup path for Seamless Co-op.
2. Download From Nexus Manually
Open the Seamless Co-op page on Nexus Mods. Open the Files or Download tab, select the current file, and choose MANUAL DOWNLOAD.
You do not need Nexus Mods Mod Manager for this install. Older instructions mention the Nexus Mods App, but the current ERSC docs send users to MANUAL DOWNLOAD, and Nexus discontinued its newer cross-platform app in January 2026.
3. Place the Files in the Game Folder
Open Steam, go to Library, right-click Elden Ring, and choose Manage. Select Browse local files, then open the Game folder.
Extract the downloaded Seamless Co-op archive into that Game folder. A current manual install uses ersc_launcher.exe and the SeamlessCoop folder.
Updating from an older Seamless Co-op install? Delete launch_elden_ring_seamlesscoop.exe and the old SeamlessCoop folder first. Then extract the current archive into the same Game folder.
4. Set One Password for the Group
- 1.Open ELDEN RING\Game\SeamlessCoop.
- 2.Open ersc_settings.ini in Notepad.
- 3.Edit only the value after =.
- 4.Set cooppassword = to the same password for every player.
- 5.Save the file.
- 6.Restart the game after any password change.
The host's settings control world scaling, invasions, rot and death debuffs, and spirit summons. Set the host's ersc_settings.ini file to match how the group wants to play.
5. Launch and Join the Session
Do not start Seamless Co-op with the normal Elden Ring button in Steam. Keep Steam online, then run ersc_launcher.exe from the Elden Ring Game folder.
Start the game with ersc_launcher.exe. Rest at a Site of Grace to receive the Seamless Co-op items.
The host uses Tiny Great Pot, and joining players use Effigy of Malenia. Use Separation Mist to leave the session, and use Judicator's Rulebook to toggle friendly fire and PvP modes.
Seamless Co-op supports up to 6 total players according to the ERSC FAQ: the host plus 5 others. When the host uses Separation Mist, the session disbands.
6. Add It on Steam Deck or Linux
Steam Deck and Linux use the same Seamless Co-op files, then run the Windows launcher through Proton. Install the files into Elden Ring's Game folder first.
On Steam Deck, switch to Desktop Mode. In Steam, click Add a game in the lower-left corner, then add ersc_launcher.exe as a Non-Steam game.
Open the new ersc_launcher.exe entry's Properties. Open Compatibility, select your preferred Proton version, and ERSC says Proton 8.0 or Proton 7.0 should work fine if you are unsure.
7. Copy an Existing Character
Vanilla Elden Ring saves use .sl2. Seamless Co-op uses .co2.
On Windows, open File Explorer. Click the address bar, enter %appdata%/EldenRing/, then open the numeric SteamID folder.
Copy ER0000.sl2. Paste a copy in the same folder, then rename that copy to ER0000.co2.
Do not move a Seamless Co-op .co2 save back to a vanilla .sl2 save; the Nexus page warns that this can get you banned.
8. Fix Setup and Connection Problems
Missing items or crashes: open Steam. Go to Library, right-click Elden Ring, and choose Properties.
Open Installed Files. Then select Verify integrity of game files.
Inappropriate Activity Detected: the fix depends on how you launched. On a Seamless Co-op launch, antivirus is blocking the mod's hook into the game, so use only files downloaded from the official Nexus Mods page or the author GitHub mirror.
Then in Windows Security open Virus & threat protection. Go to Protection history, select the item, and choose Restore.
Then choose Allow on device after confirming the file came from the official source. On a vanilla launch, another mod has disabled EAC: remove dinput8.dll or move it out of the Game folder.
Through Mod Engine 2, redo the ERSC Seamless Modding setup. Through a randomizer, install the latest Seamless Co-op from Nexus.
Missing ersc.dll: use the latest launcher bundled with the mod. Whitelist the Elden Ring Game folder in your antivirus, and confirm ersc.dll is in the SeamlessCoop folder.
Then right-click it. Open Properties, and click Unblock if that option appears.
Error 740: right-click ersc_launcher.exe and choose Run as administrator.
Failed, no session found: confirm every player owns a legitimate Steam copy. Every player runs the same Elden Ring version (check the bottom right of the title screen) and the same Seamless Co-op version.
Every player uses the same password in ersc_settings.ini with a full game restart after any change. Every player is connected to the Steam Friends network.
Also verify the game files, and make sure nobody in the group has blocked another player on Steam. Disable intrusive anticheat such as Vanguard.
Poor connection quality: open Steam. Go to Settings, open In-Game, and then open Steam Networking.
Choose Friends only for Steam friends or choose Always. Steam Networking changes can share your IP address with people you connect with.
9. Remove It or Run It With Other Mods
To play normal Elden Ring, launch the game normally from Steam. Seamless Co-op runs when you start Elden Ring through ersc_launcher.exe.
To remove Seamless Co-op fully, open ELDEN RING\Game. Delete ersc_launcher.exe plus the SeamlessCoop folder.
For older installs, also delete launch_elden_ring_seamlesscoop.exe. All players must run the same mods to connect to each other, though visual-only mods can stay personal.
For other mods, the current ERSC docs use Mod Engine 2; note that Mod Engine 2's own repository now says its development is discontinued and future work has moved to me3, so use the ME2 workflow ERSC still documents.
Place ME2 in the Elden Ring Game folder. Put SeamlessCoop inside Game\ME2, set the password in Game\ME2\SeamlessCoop\ersc_settings.ini, and configure config_eldenring.toml with external_dlls = [ "SeamlessCoop/ersc.dll" ].
Then launch with launchmod_eldenring.bat. Do not use Elden Mod Loader, Lazy Loader, or generic DLL injectors as the Seamless Co-op launch method.
The ERSC docs say Seamless must launch through ersc_launcher.exe or ModEngine2.
Frequently Asked Questions
Can I install Seamless Co-op on console?
The verified instructions cover Elden Ring on PC through Steam. There is no documented console install path.
What launcher should I use after installing Seamless Co-op?
Use ersc_launcher.exe for Seamless Co-op. Launch Elden Ring normally from Steam when you want the unmodded game.
What does the host control in Seamless Co-op?
The host settings control world scaling, invasions, rot and death debuffs, and spirit summons.
Does Steam Networking have a privacy tradeoff?
Yes. The ERSC FAQ says Steam Networking settings can share your IP address with people you connect with.
