How to Run 8 Player Co-op on a Left 4 Dead 2 Server

To run 8 player co-op on a Left 4 Dead 2 dedicated server, install the L4DToolZ extension into left4dead2/addons, raise the client limit with sv_setmax 31 and the player cap with sv_maxplayers 8, and remove the lobby reservation with sv_force_unreserved 1, because a lobby reserved server is locked to 4 players in campaigns. Then add a SourceMod "multislots" plugin that spawns an extra survivor bot for each player beyond four, so everyone gets a character. Players join with connect in the console, not through a lobby.

The base game caps co-op at four survivors and Versus at eight players. Lifting that is a server side change only. Players do not install anything.

What you need

If SourceMod is not on the server yet, the setup is covered in how to host a Left 4 Dead 2 server.

Step 1: Install L4DToolZ

1. Download the latest release from the L4DToolZ releases page. This maintained version works by offsets rather than signatures, so it survives game updates better than the old l4dtoolz and tickrate enabler builds.
2. Stop the server.
3. Unzip the release into left4dead2/addons on the server.
4. Start the server and type in the server console:

plugin_print

L4DToolZ should be in the list. If it is not, the files are in the wrong folder, usually one level too deep after unzipping.

Step 2: Raise the limits

L4DToolZ adds these commands:

The L4DToolZ readme recommends not setting sv_setmax above 31, because values above that have crashed servers since The Last Stand update. It also recommends setting it at launch with +sv_setmax 31, or changing it only while the server is empty.

A launch line for an 8 survivor server:

./srcds_run -game left4dead2 -port 27015 +sv_setmax 31 +map c1m1_hotel

And in left4dead2/cfg/server.cfg:

sv_maxplayers 8
sv_force_unreserved 1
sv_allow_lobby_connect_only 0
sv_visiblemaxplayers 8

If your host does not let you edit the launch line, run sv_setmax 31 in the server console while nobody is connected, then change map.

Why the lobby has to go

When a group starts a game from the main menu with "Best available dedicated", the lobby reserves the server and sets the player limit to the game's own: four for campaigns, eight for Versus. The L4DToolZ readme spells it out: not removing the lobby limits the server to those numbers. With sv_force_unreserved 1, the server ignores lobby reservations entirely, and players join directly:

connect 203.0.113.10:27015

Players open the console with the tilde key, after enabling the developer console under Options, Keyboard/Mouse. To keep lobby joining for small groups and still allow big ones, the L4DToolZ author's companion plugin (l4d2_rmc) removes the lobby automatically when needed and lets players vote on the player count.

Step 3: Give extra players survivors

Raising the cap lets eight people connect, but the game still only spawns four survivors. Players five to eight end up spectating. A multislots style SourceMod plugin fixes that: when a player joins and all survivors are taken, it spawns an extra survivor bot and puts the player in control of it, and it removes spare bots when players leave.

Several versions exist on AlliedModders, usually named MultiSlots or l4d2_multislots, and some community packs bundle their own. Pick one that is still maintained for the current game version. Install it like any SourceMod plugin:

1. Upload the .smx file to left4dead2/addons/sourcemod/plugins/.
2. Restart the server, or run sm plugins load <name> in the console.
3. Check it loaded with sm plugins list.
4. Most write a config to left4dead2/cfg/sourcemod/ on first run, with settings for the maximum survivors and whether extra bots spawn with a kit.

Step 4: Balance the game for eight

The AI Director still spawns hordes and items as if for four, so eight survivors walk through a campaign. Common adjustments:

Start with the base game difficulty raised one step and add plugins only for problems you actually hit.

Versus with more players

Versus already supports eight players, four per team. Going beyond that, for example 6v6, uses the same L4DToolZ limits plus a plugin that manages larger teams. Competitive Versus players normally stay at 4v4 and spend their effort on tickrate instead, covered in how to set up a 100 tick Left 4 Dead 2 server.

Common problems

On a GamezServers server

A GamezServers Left 4 Dead 2 server gives you the file manager and SFTP to drop L4DToolZ into addons, SourceMod plugins into addons/sourcemod/plugins, and the settings above into server.cfg, plus a live console for plugin_print, sv_setmax 31 and sm plugins list. Take a one click backup before adding a batch of plugins. Eight player co-op with plugins and a few custom campaigns sits comfortably on 3 GB. For campaigns, see how to add custom campaigns to a Left 4 Dead 2 server.

FAQ

Can Left 4 Dead 2 have more than 4 players in co-op?

Not in the base game. On a dedicated server, L4DToolZ raises the limits and a SourceMod multislots plugin gives extra players survivors to control.

Do players need mods to join an 8 player L4D2 server?

No. Everything runs on the server. Players join with connect and the address in the console.

Why can only 4 people join my L4D2 server?

The server is reserved by a lobby, which caps co-op at four. Set sv_force_unreserved 1 and have players join by address.

What is the maximum sv_setmax for L4D2?

The command accepts up to 32, but the L4DToolZ author recommends 31 at most because higher values have crashed servers since The Last Stand update.