Synergy Server Hosting

What Synergy Is

Synergy is a free modification for Half-Life 2 that turns Valve's single-player story into a co-op campaign. Instead of one Gordon Freeman, a whole squad crowbars its way through City 17, crosses the coast in a buggy and an airboat, survives Ravenholm and pushes on through Episode One and Episode Two. It is listed on Steam as a mod, made by the Synergy Team, and it also supports other single-player Source campaigns.

For years the mod looked finished: version 56.16 came out in 2015 and nothing official followed. Behind the scenes the team kept working on a development branch, and when Valve's anniversary update for Half-Life 2 broke parts of the old build, they released it on 28 November 2024. The result is a much newer Synergy, with 32 player support, saved games, Linux servers and Workshop content on dedicated servers, and it has kept receiving fixes since.

What Every Player Needs

Synergy itself is free, but it uses Half-Life 2's content, so every player must own Half-Life 2 on Steam. On 15 November 2024 Valve's anniversary update put the complete Episode One and Episode Two into Half-Life 2, so a single purchase covers all three campaigns. Synergy's own site also notes that Episode Two no longer needs Episode One.

• Half-Life 2 on the player's Steam account, which now includes both Episodes.
• Synergy from Steam, free.
• Windows, Linux or a Steam Deck: Steam lists Synergy with cross-platform multiplayer, and the November 2024 update added native Steam Deck support.

How a Co-op Campaign Runs on a Server

Half-Life 2 was built for one player, so Synergy adapts each map for a group. Map-specific EDT files patch the levels: they change triggers, fix level transitions and handle the maps where the story sends you back the way you came. The 2024 update improved many of these and rebalanced a number of map-specific difficulty spikes in the Half-Life 2 campaign.

Some details make co-op smoother. Players now spawn in a vehicle on airboat levels, vehicles no longer stop when the game autosaves, and the Use key goes through other players so nobody blocks a door or a button. For groups where one player keeps racing ahead, Synergy has an antirush option, and its behaviour at the end of two canal and coast maps was fixed in December 2024.

Choosing Slots

Slots are players online at the same time. A campaign plays best with a group that can talk to each other, so most servers are small: 8 or 10 slots for a friends group, 12 for a public server where strangers drop in, and 16 for a community night. Synergy supports up to 32, but Half-Life 2's corridors and lifts get crowded long before that.

Synergy does push the Source engine in special cases. At the annual Rebel Rush event, played through the whole campaign on a special Steam branch, the team raised the limit from 127 to 255 players in November 2025 and warned of lag and the odd crash even on a top-end CPU. That is a show of strength, not a template: everyday co-op is about a small squad, which is why every plan here includes the same 5GB of RAM and the price follows the slots.

Steam Datagram Relay, Fake IPs and Finding the Server

Update 24.12.2 changed how Synergy connects. The game client now connects to internet servers through the Steam Datagram Relay by default, which hides the player's IP address from the server, encrypts the traffic and can even lower ping. Dedicated servers use anonymized IP addresses by default, which hides the server's real address and removes the need to port forward it to appear in the server browser.

There is one side effect: because of what the team describes as a possible Steam bug, servers on anonymized addresses do not show up in the Steam client's server browser, although they do appear in Synergy's in-game browser. If you would rather list the real address, add -nofakeip to the start-up options in the Commandline Manager. Players who prefer direct connections can turn off cl_sdr_prefer, which then only matters for servers with -nofakeip.

Admins, Votes and SourceMod

Synergy is a Source mod, so the familiar server tools apply: server.cfg for the basic settings, a password if you want a private game, and MetaMod with SourceMod for admin menus, kicks and bans, and plugins. Synergy's December 2024 update fixed MetaMod and SourceMod on Linux and made newer versions work, so you can use current builds.

Synergy has its own vote menu for changing maps, and the 2024 update removed the cheat flag from some useful commands. Commands that change the game world are best kept to admins: the January 2025 update, for instance, made showtriggers_toggle server-only.

1. Stop the server.
2. Upload MetaMod and SourceMod into the Synergy folder with the File Manager or SFTP.
3. Add yourself to SourceMod's admin list.
4. Start the server and check the console for the plugins loading.

Workshop Maps and Custom Campaigns

Synergy's Steam Workshop opened in December 2014, but for ten years add-ons only worked for clients and listen servers, because dedicated servers could not use Steam's newer Workshop system. The anniversary update brought Workshop support to dedicated servers, and a December 2024 fix stopped items sometimes failing to mount. Players subscribe in Steam or in game, and Synergy mounts new items the next time a level loads.

Workshop items come in two kinds: add-ons, which sit beside the base content, and item replacements, which override it. Add-ons such as maps and campaigns are what most servers use. Replacements change how the game looks or sounds for everyone, so agree on them with the group first.

Saved Games, Updates and Rollbacks

Saved games are the biggest change for a hosted server. A host can load a saved game, and friends who were connected when it was made are restored when they join, on dedicated servers too. A full run of Half-Life 2 and both Episodes takes many evenings, so a long-running server with saves is the natural home for it. Settings and saved games also sync through Steam Cloud on the client side.

Updates come from two directions: Synergy itself and Half-Life 2. After either one, run Steam Update and restart. If an update ever causes problems, the team keeps the previous version on a Steam beta branch called 56.16 and notes that it pairs with Half-Life 2's steam_legacy branch. Take a backup in the Backup Manager before any switch, so configs, plugins and saves are safe.

What to Compare Before You Rent a Synergy Server

Most Synergy hosting looks alike on paper. These are the details that decide whether the campaign runs smoothly.

1. File access for SourceModYou need SFTP or a file manager to install MetaMod, SourceMod and custom maps.
2. Start-up optionsCheck that you can set launch options such as -nofakeip yourself.
3. Updates after Half-Life 2 changesValve updates can affect Synergy, so a one-click update matters more than it seems.
4. Backups you can restoreLook for snapshots you can take and restore yourself before trying new plugins.
5. Locations near the squadPing decides firefights. Test from where your players are.
6. Billing termsCompare monthly and longer terms, and look for setup fees or minimum contracts.

Synergy Server Glossary

Synergy

A free Half-Life 2 mod that adds co-op play to the Half-Life 2 series and other Source campaigns.

Source engine

Valve's engine behind Half-Life 2, and the base Synergy runs on.

EDT file

A map-specific file Synergy uses to patch a Half-Life 2 level for co-op.

Steam Datagram Relay

Valve's relay network, which Synergy uses to hide IP addresses and encrypt traffic.

-nofakeip

A start-up option that makes a Synergy server show its real IP address again.

SourceMod

A plugin platform for Source servers, used for admin menus and custom features.

Antirush

A Synergy option for groups where players race ahead of the team.

Rebel Rush

Synergy's annual event playing the whole campaign with a very high player count.

Synergy Server Help and Next Steps

Useful pages for setting up and running your server.

• Synergy on SteamFree download, requirements and news.
• Synergy: Half-Life 2's 20th Anniversary UpdateThe full list of changes from November 2024.
• Synergy 24.12.2 UpdateSteam Datagram Relay, fake IPs and -nofakeip.
• Gaming Deluxe control panelWhat the panel does and how to log in.
• Our server locations
• Contact support24/7 help with setup, SourceMod and updates.