Project Zomboid Multiplayer: Build 41 vs Build 42 (42.19)
Build 42.19 · Host and dedicated multiplayer work on both Build 41 and Build 42
Which build should you play multiplayer on?
Both branches can host friends. The real choice is stability and content, not “MP available or not.”
Prefer Build 41 (stable)
- Long-running servers, public RP, and large mod lists that still target 41.x.
- Fewer mid-season world-breaking patch risks than Unstable.
- Most older guides, collections, and host panels assume this branch.
Prefer Build 42 (unstable, e.g. 42.19)
- Animals, expanded crafting chains, map and systems work that B41 never received.
- Friends who already play Unstable and accept patch resets or save risk.
- Testing Host/dedicated setups for the systems that will carry into future Stable.
Current multiplayer status (B41 vs B42)
| Topic | Build 41 (stable) | Build 42.19 (unstable) |
|---|---|---|
| Host / listen server | Yes — Host from the main menu | Yes — Host and multiplayer UI present |
| Dedicated server | Yes — Steam tool / StartServer scripts | Yes — same general workflow; install and branch must match clients |
| Invite / server browser / IP join | Yes | Yes (Steam invite, browser, and IP paths exist in client UI) |
| Default game port | DefaultPort=16261 (UDP; configurable) |
|
| Steam-related UDP option | UDPPort=16262 (Steam section of server options; configurable) |
|
| Mod ecosystem | Very large, mature for 41.x | Growing; many packs need explicit B42 builds |
| Risk profile | Stable content baseline | Frequent patches; 42.x worlds can break across major unstable jumps |
Older guides from early Build 42 (when multiplayer was still off) are outdated for current Host and dedicated play. Local couch split-screen still works when everyone is at one PC; it is not a substitute for real multiplayer networking.
Host, dedicated, LAN, and join paths
Option 1 — Host (listen server)
Best for a short co-op session. The host machine runs the world and a player client together. When the host quits, the session ends for everyone.
- Launch the same Steam branch as your friends (Stable 41.x or Unstable 42.x).
- Open Host, create or load a server preset, set name/password, sandbox, and memory if offered.
- Start the world, then invite via Steam or have friends find the public/LAN listing.
- Keep the host PC awake; sleep, VPN changes, or closing the game drop the server.
Option 2 — Dedicated server
Use a dedicated process when the world should stay online without a player sitting in Host. On Steam, install Project Zomboid Dedicated Server (Tools), or use the game’s start-server scripts on the same install/branch you want clients to use.
- Start once so config files generate under the user Zomboid folder (commonly
Server/<name>.iniand sandbox vars). - Edit the INI for name, password, public listing, PVP, mods, and ports (see below).
- Forward or UPnP the ports you actually configured, then start the server and confirm the log shows the intended values.
- Players join by public list, favorites, or IP +
DefaultPort.
For memory sizing, admin options, and load monitoring, use the server memory guide and the server administrator tips.
Option 3 — Same LAN
On one network, Host or dedicated usually appears under the LAN browser. Clients still need the same build and mod set. Router port forwarding is not required for pure LAN; host firewall rules for the game/server process still matter.
Ports, UPnP, Steam Relay, and custom values
DefaultPort and UDPPort. There is no DefaultPortPlusOne field. Do not open a long “one UDP port per player slot” range such as 16263+ based on old articles. Forward (or UPnP) the ports your INI actually lists.
| Option | Default | What it is for |
|---|---|---|
DefaultPort |
16261 |
Primary game connection port players use when joining by IP/port. |
UDPPort |
16262 |
Steam-related UDP port in server settings (Steam section of the options UI). |
UPnP |
Typically on by default | Asks a UPnP-capable gateway to map ports automatically. Useful for home internet hosting; not a LAN feature. |
DefaultPort=16261
UDPPort=16262
UPnP=trueCustom ports
You may change either port if your host requires it. Whatever you set must match on:
- the server INI (or Host preset),
- router forwards / cloud security groups,
- the port friends type when joining by IP.
Steam vs non-Steam and Relay
- Steam clients can use the public list, Steam invite, and optional Steam Relay on the join/account UI when a direct path fails (higher latency, but bypasses some NAT issues).
- Direct IP join still needs the correct
DefaultPort(and a reachable host). Relay is not a replacement for fixing wrong ports. - Dedicated hosting panels may show different default numbers—always trust the values written into the running server’s INI and startup log over third-party templates.
DefaultPort / UDPPort. Then check the server console and client log rather than deleting world folders first. Related: server initialization stuck and connection troubleshooting guides on the site.
Feature differences that matter in co-op
Multiplayer works on both branches; gameplay systems do not. These differences drive most “should we move the friend group?” decisions.
Animals and late-game food
Build 42 adds livestock, wildlife, tracking, and longer renewable loops. Co-op roles for hunting, herding, and base logistics matter more than on B41’s farm-and-loot loop.
Crafting depth
B42 expands production chains (metal, pottery, clothing, stations). Groups benefit more from specialization; B41 still allows broad self-sufficiency with less tooling.
Combat and PVP
B42 revises ranged ballistics and many combat feel changes. Expect different gunplay and friendly-fire risk. PVP still depends on server Safety/PVP options, not on “MP being unlocked.”
Map and world systems
Unstable map, basement, and town coverage continue to evolve. Hosts should label the exact 42.x patch and warn that major unstable jumps may not keep old worlds.
Co-op habits that work on both
- Agree on sleep, PVP, safehouse, and loot-respawn rules before the first death.
- Split skill books early so the group covers more professions.
- Drive carefully in MP: car desync still punishes bumper-to-bumper multi-vehicle caravans.
- Use voice chat when clearing towns; text alone is slow under pressure.
Mods and version matching
Server and every client must share the same enabled mod set and compatible Workshop builds for that branch. A B41-only collection will not load correctly on a B42 server.
- Build 41: huge mature library; still the default for public RP and heavy content packs that never left 41.
- Build 42: prefer mods that explicitly list your 42.x range. Prefer fewer, actively maintained packs over huge untested stacks on Unstable.
- Moving a community: treat B41 → B42 as a new season. Recreate the server, rebuild the mod list for B42, and do not expect seamless world conversion.
Always check the Workshop page for compatibility notes against your exact build string before enabling a pack.
Launch checklist
- Pick one branch for the group: Stable 41.x or Unstable 42.x (document the full version string).
- Install matching client (and dedicated tool/scripts if used) on that branch only.
- Decide Host vs dedicated; create a named server preset / INI.
- Set
DefaultPort/UDPPortdeliberately; forward those UDP ports or rely on working UPnP—not invented per-player ranges. - Lock mods and sandbox; test with one non-host account before inviting everyone.
- Publish rules for PVP, safehouses, admin powers, and wipe policy.
- Back up the full server user-data tree (config + multiplayer saves), not only the INI file.
Related pages: server administrator tips, server memory, admin access, server mods.
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