Smash Ultimate PC online multiplayer

WindowSmash multiplayer

Each PC needs its own save and netplay_id.txt. Match the WindowSmash build, selected game version and DLC. Windows uses the launchers named below; native Linux uses the corresponding .sh scripts in the launcher table.

Create a room in the online lobby

1. Open Play SSBU.bat on each Windows PC, or ./play-ssbu.sh on Linux.
2. Allow the game's firewall prompt if it appears and you intend to connect.
3. Check the connection overlay with F1 on Windows.
4. On the host, choose Local Wireless → Create a Room.
5. On each guest, open Local Wireless → Rooms List.
6. Select the host's room when the list refreshes.
7. On the host, accept each friend's join request.

After connecting to the lobby, the host still needs to choose Create a Room. Use smash.recomps.wtf:39421 on every PC.

Keep friends in one lobby group

A lobby code filters who sees the same rooms. It is case-sensitive and is not a password.

1. Open Esc → Online on each Windows/Linux build with the settings menu.
2. Select Play online in a private lobby.
3. Enter the same Lobby code on every PC.
4. Choose Restart now on every PC.
5. Create or join the in-game room with the lobby steps above.

For a build without that menu, close the game and edit the first non-comment line of online_server.txt in the project root to the same server followed by a space and your agreed code. For example, append our-friends after the server address. Save the file, relaunch, then create/join the Local Wireless room. Do not use an example code as a secret.

Direct connections through the lobby

The lobby automatically attempts a direct UDP path between players and relays traffic if it cannot connect directly. After joining, the overlay reports direct or relayed. A relayed connection can still work.

For relay-only play:

1. Open Esc → Online.
2. Turn off Direct connections.
3. Restart the game.

Without that menu, close the game, put off in root online_direct.txt, then relaunch. This is separate from hosting a private address-based room below.

Host a private room by address

1. Open launchers\Host SSBU Netplay.bat on the host PC.
2. Enter the host's player name at the first prompt.
3. Enter the agreed room name at the next prompt.
4. Press Enter at the UDP-port prompt to keep 39420, unless you deliberately use another port.
5. Allow incoming UDP for the chosen port when the firewall asks.
6. Copy the host's own address:port from the launcher window or netplay_address.txt.
7. Send that address and the exact room name to your friends.
8. Open Local Wireless → Create a Room in the game.
9. Accept the guests' join requests.

The launcher tries UPnP to open the host port. If it fails, choose the reachable address/path in the table below. This private mode routes players through the host; it is not the lobby's automatic player-to-player direct mode.

Join that private room

1. Open launchers\Join SSBU Netplay.bat on the guest PC.
2. Enter the host's address:port at the first prompt.
3. Enter your player name.
4. Enter the room name exactly as the host supplied it.
5. Press F2 in the game to check that the relay is reached.
6. Open Local Wireless → Rooms List.
7. Select the host's room.
8. Wait for the host to accept.

If asked for a Smash Tag, make your own. Guests do not need to change router forwarding.

WindowSmash Linux launchers

Run the appropriate command from its unpacked project/package folder, then use the same host, guest and in-game actions above.

Choose the launcher row for your installation. Mac cross-platform networking still needs testing.

OpenSmash online on Windows

On Windows, you can host and join through the lobby, LAN or a room code. Linux has no online mode. Match the OpenSmash source/runtime build, game version, fighters and mods on both ends. Testing so far used two instances on one PC; internet connections between PCs, real-router UPnP and STUN still need testing.

Choose a connection and display name

1. Open Play SSBU.bat.
2. Press F1 to open the Vulkan settings menu.
3. Select Experimental.
4. Set Your name to the name you want other players to see.
5. Turn Online play on.
6. Choose one of the connection modes below.
7. Select Restart the game now after changing the mode.

If F1 is unavailable because the menu is disabled, close the game, set menu = on in the install location's config/graphics.ini, then relaunch. A build without the menu must use that file for the network settings in the table. An empty player name can use your Windows username.

Change file settings with the game closed, then restart. The launcher's run.py clears inherited SSBU_* variables, so use config/graphics.ini for these network settings.

Create and join through the public lobby or LAN

1. Select Lobby server on every PC, or Same network (LAN) on every PC in the same home network.
2. Restart each game after changing that choice.
3. On the host, open Local Wireless → Create Room.
4. On each guest, open Local Wireless → Rooms List.
5. Select the host's room.
6. On the host, accept the wants to join! request.
7. On both sides, select the stage and fighter.
8. On the host, press L+R to start.

Allow the game's firewall request if prompted. LAN uses UDP 39501 for discovery plus a random UDP port for the session. LAN and lobby participants must use the same online_code in config/graphics.ini; the default is public.

Use a friends-only lobby group

1. Close OpenSmash on each PC.
2. Set online_code = our-friends in each install location's config/graphics.ini, replacing the example with your agreed code.
3. Start each game in Lobby server mode.
4. Use the create/join steps above.

This lobby-group code is different from the host-generated room code below. It filters the group and does not authenticate friends.

Host and join a private direct room

1. On the host, choose F1 → Experimental → Host a room.
2. Restart the host game.
3. Copy its ROOM CODE, or read ROOM CODE on an [online] line in its run log if the menu does not show it.
4. Send that code to the guest.
5. On the guest, choose Join with a code.
6. Enter the host's code.
7. Restart the guest game.
8. Create/join the in-game room using Local Wireless, as above.

The host tries UPnP for UDP 39500. If the router does not allow it, the host needs that UDP port forwarded to the PC. If connection still fails and the guest log prints your code, the host can put that code in online_peer in config/graphics.ini; both then restart. Otherwise return both sides to the public lobby, which attempts a direct connection and can relay traffic.

If a room does not appear

WindowSmash's run log is build/play.log. OpenSmash's Windows run logs are <install location>/logs/game_*.log. Keep names, IP addresses and local paths private when sharing logs; network troubleshooting expands diagnosis.

Limits, privacy and rollback

WindowSmash's current Quickplay is a separate service experiment: login, search and two players matching into a room worked on one PC. Full matches, larger rooms, results and GSP still need testing. It is not required for the friend-room steps above. Nintendo matchmaking, accounts and rankings are unavailable.

Neither protocol offers authentication or encryption. Lobby-group codes are not passwords. WindowSmash's automatic direct connections expose an IP address to connected room members; its private rooms go through their host. Use its relay-only steps above if that matters to you. For OpenSmash lobby relay-only play, close the game, set online_direct = off in config/graphics.ini, then relaunch.

OpenSmash Windows: optional rollback test build

Normal sessions use delay-based networking. Windows has a separate, opt-in rollback test build; it is still in development. The switch needs its matching ssbu_game_r1.dll and ssbu_native_rb.exe, and both players must use the same project version and game update with rollback enabled. Use source eac10a1 from the version table below to build this option.

1. Close the game.
2. Open Install SSBU.bat.
3. Tick Rollback netcode for online play.
4. Press Install or Resume to complete the extra build.
5. Start the game with Play SSBU.bat.
6. Open F1 → Experimental.
7. Turn Online play on.
8. Turn Rollback netcode on.
9. Close the game.
10. Start it again with Play SSBU.bat.
11. Check for Rollback netcode on: ssbu_native_rb.exe + ssbu_game_r1.dll in the launch output to confirm the test build was selected.
12. Have your friend make the same version and enablement checks before using the Local Wireless room steps above.

The extra compile takes about as long as the initial compile. If the switch is disabled and asks for the rollback build, return to the installer to build it. If either paired file is missing at launch, the launcher reports the missing build and starts the ordinary game instead. The launch output and F1's Rollback is active in this run message only describe the startup choice; use the match's log entries to check for a later fallback.

Check your first Local Wireless match, and repeat this check for later matches:

1. Enter a Local Wireless match using the room steps above.
2. Open that run's log through F1 → Log, or open its <install location>/logs/game_*.log file.
3. Search that match's entries, ignoring case, for rollback OFF for this match or ran WITHOUT rollback in the match report.

Either message means that match has fallen back to delay-based play because there was not enough memory for its saved rollback states. You can continue playing with delay-based networking. To stop using the test build instead:

1. Leave the current match.
2. Turn Rollback netcode off under F1 → Experimental.
3. Close the game.
4. Start it again with Play SSBU.bat.

The recorded rollback test used two games on one PC with simulated 150 ms ping and loss. Real internet sessions remain experimental, and rewinding three or more frames can hitch. Keep the normal delay-based path when you do not want this optional Windows test.

Versions covered by this guide

WindowSmash’s main lobby is smash.recomps.wtf:39421; the older 39420 lobby does not provide the same Quickplay service.

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