Factorio Version Mismatch Fix ("Version mismatch detected!")

The Factorio error "Version mismatch detected!" means your game and the server run different versions, and Factorio only lets players join when the versions match exactly. The fix is to update whichever side is behind, or pick the server's version in Steam under Properties, Betas. The related "Mods mismatch detected!" means a mod version differs, which the Sync mods with server button fixes in most cases.

Short answer

• You are newer than the server: ask the owner to update the server, or switch your game to the server's version in Steam Betas.
• You are older than the server: update Factorio. In Steam, check you are not stuck on an old beta.
• Stable vs experimental: everyone, server included, must be on the same branch.
• "Mods mismatch detected!": use Sync mods with server when joining, or match the mod versions in mods/mod-list.json on the server.

Why Factorio is so strict

Factorio is deterministic: every player runs the whole simulation on their own machine, and the server keeps everyone in lockstep. If two players ran even slightly different versions, their factories would drift apart and desync. So the version check is exact, down to the last number. "2.0" is not enough, it has to be the same full version, such as 2.0.77 on both sides.

The message looks like this:

Version mismatch detected! The server is running an older version of the game.
You are running version 2.0.41. Server is running version 2.0.35.

It tells you which side is behind, which makes the fix easy to pick.

When it happens most

• After a Factorio patch. Steam updates players automatically, the server stays on the old version until someone updates it.
• Experimental vs stable. Wube ships new versions to the experimental branch first. In 2026, with 2.1 on the experimental branch while 2.0 stayed stable, groups often had one player opted in to experimental and everyone else on stable.
• Standalone vs Steam. A copy from factorio.com updates separately from Steam copies.

Fix 1: Update the server

On a self hosted headless server, download the matching version and replace the files:

wget -O factorio-headless.tar.xz https://www.factorio.com/get-download/stable/headless/linux64
tar -xJf factorio-headless.tar.xz

Stop the server first, and keep your saves, mods and data/server-settings.json. Replace stable with latest in the URL for the newest experimental build, or with an exact version number to pin one, for example 2.0.77. Start the server and check the version in the first lines of the log.

Fix 2: Switch your game to the server's version

When the server intentionally stays on an older version, for example because a big mod has not updated yet:

1. In Steam, right click Factorio and click Properties.
2. Open Betas.
3. Pick the branch that matches the server's version from the list.
4. Let Steam download it, then connect.

Set Betas back to None when you want the current stable version again. Players with the standalone version can download older versions from their factorio.com account.

Fix 3: Mods mismatch

Factorio also checks every mod version. When you join a modded server, the game compares your mods with the server's and offers to sync:

1. On the error screen, choose Sync mods with server.
2. Factorio downloads the exact mod versions from the mod portal, and disables mods the server does not use.
3. Restart the game when asked and join again.

Syncing only works for mods published on the mod portal. If the server runs a private or edited mod, every player needs that exact file. If sync fails, check mods/mod-list.json on the server and the mod zip file names, which include the version number.

Syncing switches your enabled mods to match the server, so re-enable your own mods afterwards if you want them for single player.

Fix 4: Space Age content

Space Age, Quality and Elevated Rails are handled like mods. If the server has them enabled in mod-list.json, every joining player needs to own Space Age. A player without the expansion cannot join a Space Age map, no matter which version they run.

Keep the group in sync

• Agree as a group whether you play stable or experimental. Stable is the safer choice for a shared server.
• After each patch, update the server first, then tell everyone.
• For modded servers, wait until your key mods support the new version before updating anything.
• Back up the save before every update. Moving a save to a newer version is fine, going back to an older version is not.

Skip the update chores

A Factorio server from GamezServers runs the headless server for you, with a one click Backup before updates, a file manager for mod-list.json, and an address friends can paste straight into Connect to address. Setting one up takes about a minute, see how to host a Factorio server.

FAQ

What does "Version mismatch detected!" mean in Factorio?

Your game and the server run different versions. The message says which one is older.

How do I downgrade Factorio on Steam?

Right click Factorio, open Properties, go to Betas and pick the older version.

Can players on stable join an experimental server?

Only if both happen to be on the exact same version, which is rare. Keep everyone on one branch.

Do players need to download mods before joining?

No. Sync mods with server downloads the exact versions from the mod portal.