Understanding Multiplayer in The Sims 4
The Sims 4 doesn't have official multiplayer. What most people are actually talking about is the TS4Multiplayer mod, which has been around since 2016. It lets multiple players control different Sims in the same save file through a host-based system. The Sims 4 Gameplay Lore Explained Multiplayer concept is really just explaining how this mod interacts with the base game's systems, not any built-in EA feature. The mod works by creating a local server that routes player inputs. One person runs the game as the host and loads or creates a save. Other players connect through the mod's interface using a shared network code. Each client controls their assigned Sim independently while the host's game runs the actual simulation. I've run multiplayer sessions for about four years now, mostly with a small group of five people. The biggest issue nobody warns you about is that the host's computer does almost all the heavy lifting. If the host's machine struggles to run the game at all, everyone else experiences lag regardless of their own hardware. I learned this the hard way when a friend's laptop couldn't maintain more than 15 FPS running the mod, and three of our five players quit mid-session because the desync was unbearable.
There's a specific problem with how the mod handles object interactions across clients. When two players try to use the same object simultaneously, the game usually resolves it by giving priority to the host's input. This means the host can accidentally block other players from doing things. I found that designating a dedicated "object manager" role for the host, where they intentionally avoid certain rooms during group scenes, reduces friction significantly. It's not a perfect workaround but it cuts down on the arguments that normally break up sessions. The save file format matters more than most guides mention. The multiplayer mod expects standard .save files but gets confused by certain expansion pack features, especially traits and aspirations that were added in later patches. I've had saves corrupt after mixing Sims with custom traits from multiple packs in a multiplayer context. My fix has been to keep multiplayer saves separate from single-player saves and never install new patches between sessions without testing first. Network connectivity is another area where beginners get stuck. The mod supports both LAN and internet connections, but internet play requires port forwarding on the host's router. I spent two weeks troubleshooting with a friend before realizing our ISP was using carrier-grade NAT, which blocked the connection entirely. We ended up using a VPN relay through a third party to make it work. If someone tries this over the internet and it fails, checking for CGNAT should be one of the first things you investigate.
The mod has been largely abandoned by its original developer. The last significant update was around 2021, which means it may not support every recent patch of The Sims 4. You need to match your game version to what the mod supports, and there's no guarantee that future updates will work together. EA's regular patches often break compatibility temporarily until the mod gets updated again. Installation is straightforward if you follow the current documentation on GitHub. You download the mod files, place them in your Mods folder, and launch the game with script mods enabled in the settings. Non-host players need the mod installed but don't need the full game if they're using the standalone client version. The host still needs ownership of all relevant expansion packs used in the save file. Performance impacts are real and often underestimated. Running the mod adds approximately 20 to 40 percent overhead to the host's CPU usage compared to normal gameplay. Memory consumption increases by roughly 500MB to 1GB depending on the number of connected players. I typically close all background applications on the host machine before starting a session to avoid frame drops.
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The mod doesn't support all custom content. CC that modifies core game scripts can cause desynchronization between clients, where one player sees an object in a different state than another player. I recommend testing any new custom content in single-player before introducing it to a multiplayer session. If it crashes or behaves oddly there, it will absolutely cause problems across the network. There's also the matter of communication. Since players are in separate windows controlling individual Sims, coordinating actions requires voice chat or text communication outside the game. I use Discord with screen sharing for complex sessions, which helps players see what others are doing without relying on in-game chat that doesn't exist in this mod. Ultimately, the system works well enough for casual sessions but has enough friction points that it frustrates people expecting a polished multiplayer experience. It's not broken, it's just built on top of a game that was never designed for this use case, and you can feel that in almost every interaction.
