Casualties Unknown Multiplayer and Casualties Together
Co-op is a mod-driven experience, not a built-in lobby. That means the session starts before anyone launches the game: same build, same loader, same mod list.
Quick answer
- Multiplayer runs through a community co-op mod, not an official matchmaking service.
- Every player needs the same game build, loader version and co-op mod version.
- Host first, then have players join; a late join with a different mod list usually fails.
- Plan one short session before a long one so version problems surface early.
What Casualties Together is
Casualties Together is the community co-op layer players use to share a Casualties Unknown session. It is not an official publisher feature. That distinction matters for support: problems are solved by matching versions and reading logs, not by waiting for an official patch.
Because it is community-maintained, the mod can lag behind a game update. If the game updated today and the co-op mod did not, the correct move is to wait or roll back, not to force a mismatch.
What every player needs
| Item | Requirement |
|---|---|
| Game build | Identical on every machine |
| Mod loader | Same loader family and compatible version |
| Co-op mod | Same release version |
| Other mods | Either identical or explicitly confirmed compatible |
| Network | Host reachable; no restrictive firewall blocking the session port |
Write the versions into the session invite. "Latest version" is not a version.
Session setup checklist
- Update the game on every machine and launch it unmodded once.
- Install the loader and confirm the log file is written.
- Install the co-op mod from its published page, at the same version for everyone.
- Host a short test session. Two players, five minutes, one fight.
- Add the rest of the mod list only after the test session works.
- Record the final list in the group chat so the next session is reproducible.
Why a join fails
Most join failures fall into four buckets:
- Version mismatch: the most common cause. Compare the exact mod and loader versions.
- Load order: a dependency loaded after the mod that needs it.
- Firewall or NAT: the host is not reachable from outside the local network.
- Corrupt install: a partially copied mod folder or two versions in the same directory.
Test in this order: unmodded launch, loader log, co-op mod version, then network. Changing several at once hides the cause.
Running a session that people finish
Co-op amplifies the beginner mistakes from the solo guide. Agree on a few rules before the first room:
- One person calls the retreat. Debate mid-run gets people killed.
- Share light and medical supplies before someone needs them.
- Do not split up in an unfamiliar area on the first session.
- End on a survived run, not on a wipe. Morale is a resource.
If the session desyncs, stop and compare logs before rejoining. Repeated reconnects usually make the state worse.
Run this checklist
0 / 6 doneFrequently asked questions
Does Casualties Unknown have official multiplayer?
Co-op is provided by the community Casualties Together mod, not an official matchmaking service. Treat it as a mod with version requirements.
Why can't my friend join my session?
Check the game build, loader version and co-op mod version first, then the host firewall. A mismatch is the most common cause.
Can we use other mods in co-op?
Yes, if every player runs the same set or the mod author confirms compatibility. Otherwise expect desyncs and failed joins.
How many players can join?
The supported player count depends on the co-op mod release. Check its published page rather than assuming a number.
Does co-op progress save?
Save behaviour depends on the mod and the host. Confirm the expected behaviour with the group before a long session.
Match versions before you invite anyone
A five-minute unmodded test session saves an hour of join failures.