Factorio 2.1 on a Dedicated Server: Running the Experimental Build Safely

Factorio 2.1 is out, but only as an experimental release. Wube shipped it on 26 June 2026, and as of 28 September 2026 it is still not marked stable: the official release feed lists stable at 2.0.77 and experimental at 2.1.20. Wube hasn't given a date for stable. They said they would keep 2.1 experimental "over the whole summer … so that mod authors will have plenty of time to update", and in the release post added that "we still have plenty of time before we plan to mark it stable".

So the question for a server owner isn't how to upgrade to Factorio 2.1. It's whether to run the experimental build now, and if so, how to do it without stranding your main world. This page covers both, using the Factorio egg your server actually runs.

The short version

Your server can run 2.1 today: set Factorio Version to experimental and reinstall. Before you do, know that a save opened in 2.1 can't go back to 2.0, that every player must opt into the same build, and that only part of the mod portal has caught up. For a world you care about, test on a copy first.

What 2.1 Actually Changes

Wube framed 2.1 in its 29 May plan post as a refinement release, not an expansion. In their words it is "mostly: Quality of life, Some small features, Fixes and game polish, Modding improvements", with an explicit list of what it doesn't add: "No new planets, No new enemies, No new research trees or resource chains." It applies to the base game and Space Age alike.

Two more things from Wube matter if you run a server long-term:

• It is meant to be the last major update. The same post: "We envision 2.1 as our last major update of Factorio, and we will shift the focus onto long term support." Whatever version your campaign ends up on, 2.1 is where the mod ecosystem will eventually settle.
• The Linux requirement change doesn't touch servers. 2.1 raised the desktop Linux minimum to GLIBC 2.36, but the release post notes "Headless and Steam versions are not affected."

How the Version Field Resolves 2.1

Your server's version is set by the Factorio Version field on the Startup tab. The egg's install script reads Wube's feed at factorio.com/api/latest-releases and resolves the value once, at install time:

The field's own description warns that changing it "will require a full server reinstall". Two consequences follow, and both catch people out:

• experimental is a pointer, not a version. It pins whatever 2.1 build was current when you reinstalled. Wube keeps shipping 2.1.x builds, and players on Steam's experimental branch update automatically. The server doesn't, so after the next build your players can't join until you reinstall.
• Stable 2.1 won't arrive by itself. When Wube eventually marks 2.1 stable, a server left on latest stays on its 2.0 build until someone reinstalls it. Nothing moves on its own.

Pin the number when your group is settled

For a test server, experimental is convenient. For a group that wants predictable sessions, set the exact build (for example 2.1.20) and change it deliberately when everyone updates together.

Saves: One-Way Into 2.1

Wube is clear about the direction: "2.0 save games will load, but there may be changes that break your factory designs … Once updated, blueprints and save games cannot be downgraded to 2.0."

On a server, a world starts being written as 2.1 the moment a 2.1 build loads it. The first autosave does it; the egg's default is every 10 minutes. After that, reinstalling to latest brings back the 2.0 program, but not a save it can read. The only way back is a copy of the world taken before the switch.

Mods on 2.1

Factorio mods declare one major version each. Wube's modding docs are strict: mods "can only be compatible with one major version", and a mod has to be explicitly re-marked before it counts as compatible with a newer one. A mod built for 2.0 isn't a 2.1 mod until its author publishes a 2.1 release.

The mod portal shows how far that has got. On 28 September 2026 its version filter returned 4,288 mods for 2.1, against 9,754 for 2.0. Check every mod your world depends on before you switch, dependencies included.

There's a server-specific catch here too. Every reinstall on your server, including a version change, also runs a mod updater over mods/. It updates the enabled mods in mod-list.json to their newest release compatible with the installed Factorio version, and pulls in required dependencies. That's convenient, but it means a version change also changes your mod versions. Keep a copy of mods/ from before, in case you need to roll back.

Running 2.1 Safely: The Test-Copy Method

The approach Wube itself suggests is to back up first and treat experimental as experimental. On a server, that looks like this:

1. Run /server-save from the panel Console, then download the save zip from the server root. It's gamesave.zip unless you changed Save Name.
2. Download mods/ (including mod-list.json) and data/server-settings.json if you've customised them.
3. Check your mod list on the mod portal for 2.1 releases. If something essential has none, stop here: your world isn't ready for 2.1 yet.
4. Set Factorio Version to experimental (or a pinned 2.1.x) and reinstall from Settings.
5. Upload the save as a new name, for example campaign-2-1-test.zip, and set Save Name to campaign-2-1-test. Your original download stays untouched as the 2.0 fallback.
6. Start and read the console until Hosting game at appears. Version and mod errors show up in the log first.
7. Tell your players to switch branch. In Steam: right-click Factorio → Properties → Game Versions & Betas → Experimental. Standalone installs use Settings → Other → Enable experimental updates.

If the test goes badly, set the version back to latest, reinstall, and upload the 2.0 save and mods you downloaded in steps 1 and 2. If it goes well, keep playing, but remember that the 2.0 copy is now your only way back.

A reinstall rewrites the server files

Anything you haven't downloaded should be treated as gone: saves, your edited server-settings.json, and mods/. How to Update a Factorio Server and Pin a Version covers the full reinstall sequence.

Should You Switch Now?

Factorio has no mixed-version mode. The wiki's multiplayer rule is that "All game instances need the installation of exactly the same game-versions and mods." One player on stable and one on experimental can't share a server, whichever build it runs.

Common Questions

Is Factorio 2.1 released?

As an experimental build, yes, since 26 June 2026. As a stable release, no. On 28 September 2026 Wube's release feed still lists 2.0.77 as stable, and no stable date has been announced.

Will my server update to 2.1 automatically when it goes stable?

No. The version is resolved when the server is installed. A server on latest stays on its 2.0 build until you reinstall.

Can I go back to 2.0 after trying 2.1?

Only with a save made before the switch. Wube: "Once updated, blueprints and save games cannot be downgraded to 2.0."

Does 2.1 need Space Age?

No. 2.1 updates the base game and the expansion. Whether a world needs Space Age depends on the save, just as it did on 2.0.

My friends updated and now can't join

Steam's experimental branch moved to a newer 2.1.x than your server. Reinstall the server with experimental (or the matching pinned number) so the builds match again.

What to Read Next

• How to Update a Factorio Server and Pin a Version — the reinstall sequence and the save compatibility ladder
• How to Install Factorio Mods on a Dedicated Server — major-version rules and the client mod sync
• Factorio Server Saves and Autosaves — taking the backup this page depends on

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