Bohemia keeps the experimental server as a separate Steam app, ID 1890870 (stable is 1874900). The ArthOS panel cannot put a server on it. The server runs the stable game, so an experimental server has to be hosted somewhere you control. Players would also need the experimental game, because a server checks that players run its version.
What the experimental version is
Bohemia releases test builds of the game before they reach everyone. Its news posts for these builds say “We updated the Steam and Xbox Experimental applications of the game” and ask players to leave feedback on its Feedback Tracker. On 12 October 2026 the stable version is 1.8.0.13 (3 September 2026). The experimental builds are the 1.9.0.x line. The newest experimental build in Bohemia’s news is 1.9.0.10, posted 22 September 2026 (see https://reforger.armaplatform.com/news).
Bohemia keeps two separate server downloads on Steam:
- Stable server: app ID
1874900. - Experimental server: app ID
1890870.
Both numbers are in Bohemia’s server hosting page.
Why the panel cannot do it
The server’s installer downloads the game from Steam with an app ID. The Startup tab has no app ID field, no branch field and no free-form startup argument field for Arma Reforger. So there is nothing in the panel to switch, and a Reinstall Server always installs the stable server.
A Loafhosts server cannot be moved to the experimental version, because the panel offers no way to do it.
What players need
A server checks the game version of each player who joins. Bohemia’s startup parameter -rpl-validation-version-disable turns that check off, but it works only on Bohemia’s diag executable, not the normal server. So a player would need the experimental game to join an experimental server, and a player on the stable game may not be able to join. Bohemia describes the experimental game as separate Steam and Xbox applications, so the player installs that one. See Bohemia’s news for how to get it.
If you host the server yourself
These steps are for people who run their own machine, not for a Loafhosts server. With SteamCMD, Bohemia’s way is to install the server with the experimental app ID instead of the stable one:
- Install SteamCMD.
- In SteamCMD, run these commands (replace
<dir>with your install folder):
force_install_dir <dir>
login anonymous
app_update 1890870 validate
quit- Start the server with your usual
config.json.
If you use a game server manager that supports Arma Reforger, Bohemia says to set its appid to 1890870 and validate the files.
Before you do this:
- Back up the server and its saves first. A save from another game version can be refused.
- Mods built for the stable game may not work on an experimental build.
- Bohemia posted three experimental builds in the two weeks up to 22 September 2026, so expect to update again soon.
If it does not work
- Players cannot join your experimental server. Check that they run the same experimental version, not the stable one.
- A mod fails to load. It may not be built for that version. See finding the mod that stops your server.
- You want to go back to stable. Install the stable server again with app ID
1874900. On the ArthOS panel, a server is already on stable. To bring it up to the newest stable build, see updating the server.
More about the game on our Arma Reforger page.
Sources: Bohemia wiki: Server Hosting, Bohemia wiki: Startup Parameters, reforger.armaplatform.com: News, reforger.armaplatform.com: Experimental september 24 2026