You've probably spent hours—maybe even years—building the perfect suburban nightmare or a sleek modern mansion in The Sims 4, only to realize it feels kinda lonely. It’s just you and your Sims, who are currently busy waving their arms because a plate is on the floor. For a decade, the community has begged EA for a way to play together. But while the official "Project Rene" (the next generation of Sims) promises some form of social play, we’re still stuck in a single-player sandbox right now. Or are we? Honestly, the Sims 4 multiplayer mod by S4MP is the only reason I still have the game installed. It’s a community-made bridge that lets you turn a solitary experience into something shared, even if it’s a bit janky at times.
It isn't perfect. Let's be real.
If you’re expecting a seamless MMO experience like World of Warcraft, you’re going to be disappointed. This is more like a shared fever dream. You and a friend literally control the same household in real-time. You see their cursor. They see yours. You both argue over who gets to use the shower first because the plumbing just broke. It's chaotic, it's buggy, and it's some of the most fun you can have in a simulation game once you get the setup right.
What is the Sims 4 Multiplayer Mod anyway?
Basically, the S4MP mod (Sims 4 Multiplayer Project) acts as a local or remote server that syncs game states between players. It was started by a developer named nexer (Mikhail) and has grown into a massive project supported by a dedicated community on Discord. The mod doesn't change the game's code into a multiplayer engine; instead, it tricks the game into thinking the inputs from two different computers are happening on one.
Think of it as a digital "couch co-op" where the couch is the internet.
Because of how the Sims 4 multiplayer mod works, everyone needs to have the exact same version of the game. If you have the Cottage Living expansion but your friend doesn't, things are going to break. Fast. The mod syncs the "world state," meaning if I buy a fridge, it appears on your screen too. If I tell a Sim to go to sleep, they go to sleep for you. This creates a weirdly intimate gameplay loop where communication is actually more important than the Sims' social bars.
How the syncing actually works
The mod uses a "server" application that runs alongside your game. One person acts as the host. They load the save file and "open" the doors to the world. The other players—up to 12 in the latest versions, though I'd recommend sticking to 2 or 3 for stability—join via the server's IP address.
When you're in, you share the same budget. You share the same clock. If one player pauses the game to check a notification, the game pauses for everyone. This is usually where the yelling starts. "Who paused it? I'm trying to flirt with the Goth family!" is a standard sentence in a multiplayer session.
Setting it up without losing your mind
Most people fail at the installation because they rush. You can't just drag and drop a file and hope for the best.
- The Save File: This is the most critical part. The host and the client MUST start with the exact same save file. You literally have to send your
.savefile from your Electronic Arts folder to your friend. If the files don't match 1:1 at the start, the desync will be immediate. - The Script Mods: You have to enable script mods in the game settings. Obvious? Maybe. But you'd be surprised how many people forget.
- The S4MP App: You download the launcher from the official S4MP website or their Patreon. This app handles the heavy lifting of connecting the two games.
- Firewalls: Your PC will hate this mod. It will try to block the connection. You’ll need to manually allow the S4MP app through your Windows or Mac firewall.
If you're playing over the internet (not just on the same Wi-Fi), you'll likely need a tool like Hamachi or Radmin VPN. These programs create a "Virtual LAN," making the computers think they’re in the same room. It bypasses the nightmare that is port forwarding. Honestly, Radmin is generally more stable for Sims players lately, especially since Hamachi has been acting up with modern Windows updates.
The "Everything is Broken" Phase: Dealing with Desync
You will encounter desync. It is a fact of life, like taxes or your Sim peeing themselves.
Desync happens when the host's game thinks it's 2:00 PM and the client's game thinks it's 2:05 PM. Once that five-minute gap happens, the game starts to unravel. You might see a Sim standing in the kitchen on your screen, but on your friend's screen, that same Sim is on the treadmill.
To fix this, the Sims 4 multiplayer mod has a "Resync" button. Use it. Love it.
Why travel is a nightmare
Traveling to different lots is the ultimate boss fight for this mod. In the base game, The Sims 4 isn't open world. When you go to a park, you hit a loading screen. In multiplayer, if one person travels, everyone has to go. You can't have one person at the library and one person at home. The game engine just can't handle it. If you try to force it, the server will usually crash or you'll end up in a "limbo" state where nobody can interact with anything.
Mods and Custom Content (CC)
Can you use your favorite hair mods or the "Wicked Whims" mod with the multiplayer mod?
Yes, but with a massive asterisk.
Every single player must have the exact same Mods folder. If you have a custom sweater and your friend doesn't, their game won't know how to render your Sim. Best case: they see a bald, naked Sim with "Checkered" textures. Worst case: the game crashes the moment you load in. The easiest way to manage this is to zip up your entire "Mods" folder and send it to your friend via a file-sharing service like Google Drive or WeTransfer.
Don't forget the Resource.cfg file. It's the silent hero of the Mods folder.
Is it safe?
People get worried about security when they hear "Server IP" or "VPN." The S4MP mod is safe and has a huge following, but you should always be careful about who you give your IP address to. Only play with people you actually know. If you're joining a random "Sims 4 Multiplayer" group on the internet, use a VPN to hide your actual location.
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The mod doesn't touch your game's core files in a way that would get you banned. EA generally has a "look the other way" policy toward mods as long as they aren't being sold for profit or breaking the Terms of Service. S4MP has a free version and a Patreon-exclusive early access version, which is a common (and generally accepted) model in the modding world.
Why hasn't EA made this official?
It's the million-dollar question. The truth is that The Sims 4 engine—internally known as "Sophia"—was originally rumored to be an online game called "Olympus" during its early development. When SimCity 2013 flopped due to its "always online" requirement, EA supposedly pivoted The Sims 4 back to a single-player game late in the cycle.
This left the game with a foundation that was never really meant for a solo experience, but also wasn't finished for multiplayer. That's why the Sims 4 multiplayer mod is such an achievement; it's doing something the developers themselves decided was too technically difficult to implement after the pivot.
Strategies for a better experience
If you want to actually enjoy your session, stop playing it like a normal Sims game.
- Assigned Roles: Have one person be the "Builder" and the other be the "Socialite." While one person is renovating the kitchen, the other is out meeting neighbors.
- Voice Chat: Do not try to play this without being on Discord or a phone call. You need to coordinate pauses and traveling.
- Save Often: Not just once an hour. Every 15 minutes. Use "Save As" to create a string of backups. If a save gets corrupted by a bad sync, you'll want to go back to a version from 10 minutes ago, not 10 hours ago.
- Limit the household size: Playing with 8 Sims and 4 players is a recipe for a house fire—literally and metaphorically. Start with 2 Sims and 2 players.
The mod is currently in a state where it is "playable" but requires patience. It's a labor of love by the community. It's the only way to share the weird, suburban drama of the Sims in real-time, and for many, the technical hurdles are a small price to pay for seeing their friend's Sim accidentally set the stove on fire while they're busy painting a masterpiece in the next room.
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Practical Steps to Start Playing Today
Ready to try it? Don't just dive in. Follow these steps to ensure you don't waste three hours troubleshooting.
- Audit your DLC: Make sure you and your friend own the same packs. If you have "Get to Work" and they don't, disable it in your Origin/EA Desktop settings before starting. Consistency is the only way to prevent crashes.
- Clean your Save: Start a brand new save file for multiplayer. Trying to convert a 2-year-old legacy save with 50 generations of ghosts is asking for a "Save Error 0."
- Sync the Mods folder: Use a folder syncing tool or just send a
.zipfile. If the file sizes of your Mods folders aren't identical to the byte, you're going to have a bad time. - Download the S4MP Launcher: Get it from the official S4MP site. Use the public version first to see if your connection can handle it before considering the Patreon version.
- Test on LAN first: If you're in the same house, get it working on the same Wi-Fi before trying to use a VPN for remote play. It eliminates one layer of potential failure.
- Check the Discord: If you get an error code, don't Google it. Join the S4MP Discord. The community there has seen every possible error and usually has a fix pinned in the FAQ.
Playing the Sims 4 multiplayer mod transforms the game from a dollhouse simulator into a collaborative storytelling tool. It’s messy, it’s unofficial, and it’s occasionally frustrating, but it’s the closest we’ve ever gotten to a true multiplayer Sims experience. Take it slow, communicate with your partner, and keep those save backups ready.