An "incompatible version" or "invalid version" error means the client build does not match the server build. Since V3.3.0 went stable on 5 October 2026 the single biggest cause is a version mismatch: Steam has updated the players to V3.3.0 and the server is still on V3.2.0, or one side is pinned to an older build (V2.6, V3.0, V3.1 or V3.2) and the other is not. Both the client and the server must be on the same Steam branch, and Steam's build IDs differ between branches even when both say they are "updated."
V3.3.0 has been the current stable build on the default install (Default Public Version) since 5 October 2026. V3.2, V3.1, V3.0 and V2.6 are older lines. A client on one line cannot join a server on another, in either direction. There is no cross-branch compatibility, so "we are both updated" is not enough: both sides have to be on the same branch.
The fix is to pick one branch and put everyone on it. Which branch depends on what you are running.
If you are a player who opted into a branch and can no longer join your usual server, match the server rather than the other way round.
Steam only offers the branches The Fun Pimps keep published, and old point releases do get removed. Read the live list yourself rather than trusting a guide, including this one: in Steam, right-click the game, Properties, Betas. For a dedicated server, steamcmd +login anonymous +app_info_update 1 +app_info_print 294420 +quit prints them under branches.
Checked on 17 September 2026 for the dedicated server (app 294420):
| Branch | Last updated | Use |
|---|---|---|
public | 31 Aug 2026 | Default. V3.2.0. Use this unless an overhaul says otherwise. |
v3.2.0, v3.1.0, v3.0.1 | Aug to Jul 2026 | Pinned 3.x point releases. |
v2.6 | 1 Apr 2026 | The only surviving 2.x branch. Earlier 2.x point releases have been removed, so a server pinned to one of those has nowhere to return to and must move to v2.6 or forward. |
v1.4 | Apr 2025 | The 1.0 line. |
alpha21.2, alpha20.7, and older | 2024 and earlier | Where the long-running overhauls pin. |
| Cause | What it looks like | Fix |
|---|---|---|
| Server behind on build | Server is on an older build than up-to-date clients; everyone gets kicked. | Restart the server (managed hosts update on start) or force a fresh Steam update server-side. See the server-side fix below. |
| Client behind | One or two players cannot join while others can. | Update the game in Steam, restart Steam, and verify the install. Confirm the client is on the same branch as the server. |
| Branch mismatch (stable vs experimental) | Client and server are both "fully updated" but still incompatible. | Put both sides on the same branch. This is the dominant cause during the 3.0 launch. |
On managed hosts with auto-update enabled, the server runs its Steam update automatically on every start or restart, so there is generally no separate "update game files" button - the update happens before the server boots. That means the fix for a server that is behind is almost always: restart it, and make sure the branch is set correctly first. Restarting a server that is configured for an experimental branch will keep it on that branch, so check the branch setting before you blame the restart. Once the server is on its intended branch, every player simply matches their client to that branch in Steam.
Sometimes a server flips branches (for example off an experimental branch back to default) but stays stuck on the old build, so players keep getting a version mismatch even after a restart. This is a stale Steam PICS (product info) cache: SteamCMD can report "Success! App already up to date" while silently keeping the old build. Force a fresh product-info refresh by adding +app_info_update 1:
steamcmd +login anonymous +app_info_update 1 +app_update 294420 validate +quit
A few important notes:
+app_info_update 1, SteamCMD can say "Success, No Error" while keeping the old build, which is exactly why players still see a version mismatch after what looked like a successful update.-beta flag (or -beta ""). To hold a server on V3.2 for an overhaul mod that has not moved, use -beta v3.2.0 and have every player pick the same branch in Steam. Only if you deliberately want to test a newer experimental build, add the beta flag: +app_update 294420 -beta latest_experimental validate.On top of the branch and build checks, every mod version must match on the server and the client. A mismatched or missing mod produces the same incompatible-version result. Update or remove mismatched mods so both sides load an identical mod set. Note that most V2.6 mods do not load on V3.0, so plan mod updates around your branch move.
Almost always a version mismatch. V3.3.0 has been the current stable build since 5 October 2026, and older lines such as V3.2, V3.1, V3.0 and V2.6 are not cross-compatible with it. If your client is on a different branch from the server, you get an incompatible version error even when both say they are updated. Put both the client and the server on the same Steam branch. If the server itself flipped branches but stayed on an old build, force a fresh Steam update server-side with steamcmd +login anonymous +app_info_update 1 +app_update 294420 validate +quit.
No. There is no cross-branch compatibility in either direction. A client on an older line cannot join a V3.2.0 server, and a client on an opt-in experimental branch cannot join a server on the default branch. Set your client to the same branch as the server in Steam, which for almost every server is Default Public Version.
For the default stable branch, where V3.2.0 is, update the dedicated server (appid 294420) with no beta flag: steamcmd +login anonymous +app_info_update 1 +app_update 294420 validate +quit. Only add -beta latest_experimental if you deliberately want to test a newer experimental build. On managed hosts with auto-update enabled, set the branch and restart the server, which updates before it boots. Then have every player switch their client to the same branch. To go back to stable, update with no -beta flag.
This is a stale Steam PICS cache. SteamCMD can report Success while silently keeping the old build, so players keep getting a version mismatch. Add +app_info_update 1 to force a fresh product-info refresh: steamcmd +login anonymous +app_info_update 1 +app_update 294420 validate +quit. Use appid 294420 (the dedicated server), not 251570 (the game store appid).
Steam's build IDs differ between the stable and experimental branches even when each side is fully updated on its own branch. Being updated is not the same as being on the same branch. Confirm both the client and the server are on the same Steam branch (both on Default Public Version, or both on the same opt-in branch).
+app_info_update 1