Stellar Blade Online

Tip: F6 shows the co-op status.

GAME: Stellar Blade, Steam, PC
PLAYERS: 2
LINK: Steam lobby, no server of our own
RUNS IN: UE4SS v3.0.1 Beta
LICENSE: GPL-3.0-or-later

Stellar Blade Online (SBO) is a free fan mod that adds two-player online co-op to Stellar Blade on PC. Each player plays in their own world, from their own save. Your friend's EVE appears in yours and moves as they play. She wears their outfit, with their Steam name above her.

The mod runs inside UE4SS and is made of Lua scripts and a native DLL. The two games link through the Steam client that the game already runs, so there is no other program to install and no server of our own. One player hosts, the other joins.

SBO is an experimental beta. Two PCs first played together on 2026-10-17, one on Linux with Proton and one on Windows, between Belgium and Brazil at about 240 ms ping.

Until October 2026 the mod was called StellarCoop. Its folder, its DLL and its release zip keep that name, and its console commands start with coop.

CO-OP

Test dates before 2026-11-09 are on game build 24463856, with versions up to 0.8.0.

Host a session

F5 opens the co-op menu. Its first row, Host a session, creates a Steam lobby for 2 players and opens the Steam invite dialog. The lobby is friends-only by default. In Options > Session, Who can join can limit it to the friends you invite (Invited only), or give it a 7-character join code instead of the dialog (With a code). On a controller, hold View for 1 s to open the menu.

Join a friend

KEY: F5 (menu), F8 (leave)

Your friend accepts the invite in Steam. If their game is closed, Steam starts it, and they join once their save has loaded. With a join code, they select Join with a code in their co-op menu and type the 7 characters, for example CCS-CBMH. A player who is not on your Steam friends list waits for your answer, Accept or Deny. With no answer in 60 s, they are refused. If the guest loses the connection, their game tries to rejoin for 60 s.

Your friend's EVE

STATUS: First played between two PCs on 2026-10-17, on game build 24463856. Not played between two PCs on 0.9.0 yet.

When you are both on the same map, your friend's EVE appears in your world. She moves as your friend moves her and wears their outfit, with their Steam name above her. She is display only: items, unlocks and progress stay in each game, except the consumables you send with coop gift.

Partner card and chat

A card at the top left shows your friend's Steam name, ping and map, then their HP, shield and Beta. A marker over their EVE gives their name and HP, and an arrow at the edge of the screen points to them when they are out of view. During a session, Enter opens a chat box. Chat lines stay in memory, 50 at most, and never go into a log.

Shared enemies

Experimental

NEEDS: a co-op save on both PCs
STATUS: Experimental, on by default. An early form was played between two PCs on 0.4.0 (2026-10-21). The current version is not tested in game.

While both players play a co-op save, each common enemy has one HP bar and one death in both games. Same place, same spawns and shared bosses build on it, and the host's settings apply to both games. An enemy that your friend kills in a fight you were not in stays alive in your game and gives you nothing.

Co-op saves

STATUS: Loaded in game on 2026-10-21 and 2026-10-27, and with 0.9.0 on 2026-11-09 (one PC)

On the title screen the mod asks whether to play on co-op saves: copies of your five saves, StellarBladeCoop00.sav to StellarBladeCoop04.sav. Before the first copies it backs up every save into StellarCoopBackups. Night Operation, the challenges, shared enemies and shared quests (experimental, off by default) run on the copies only. Nothing goes back to your own saves unless you export a co-op save with coop saves export, which backs up your save first. The export is not tested in game yet.

MODES

Doro races

KEY: F9 (checkpoint)
COMMAND: coop race record <name>, coop race start <name>
NEEDS: a co-op save to race
STATUS: Not tested in game yet

Record a track: type coop race record <name>, run the route and press F9 at each checkpoint, then type coop race save. Race it alone against the clock or against your friend, each racer drawn as a Doro. A race has a countdown, a timer, checkpoint markers and a ranking. It gives no reward and writes nothing to a save.

Night Operation

COMMAND: coop nightop start, coop nightop shop
NEEDS: a co-op save
STATUS: The shop screen opened in game on 2026-10-27. One solo run on 2026-10-28 spawned its waves but tracked none of its monsters. The fixes are not tested in game yet.

Night Operation is a multiplayer wave-survival mode that SHIFT UP cut before release. Much of it is still in the game files. coop nightop start sends five timed waves of the game's monsters at EVE, with an 8-minute timer and a score, alone or for both players when the host starts it. Four levels set the number of monsters, from 15 to 40 in all (20 at normal). Points from a run buy items in a seven-item shop, shown in the game's own shop screen. Three of the seven are cut items. The mod never contacts the servers the cut mode was made for.

The run adapts code from Survival Protocol by SchizoEffective, with the author's permission.

Challenges

COMMAND: coop challenge
NEEDS: a co-op save
STATUS: Not tested in game yet

Five short fights built on Night Operation's code, two of them against the game's target dummies. Four are solo. The fifth, the Shooting Range, rebuilds the game's cut shooting test, and the host can start it for both players. Each challenge keeps its best run in coop-records.txt. Challenges give no shop points.

CUT CONTENT

Content cut from the game, or shipped switched off, that is still in its files.

Cut model viewer

COMMAND: coop leviathan, coop gardener, coop tendril, coop mann, coop nier, coop orcal, coop enya
NEEDS: a co-op save
STATUS: Leviathan and the free camera ran in game on 2026-10-22, on build 24463856

Shows a cut model in front of EVE, with a free camera for filming: Leviathan, the Gardener, the Tendril, the early Mann model, three cut machines from the NieR collaboration, and prototype statues of Orcal and Enya. Nothing in the viewer can be fought.

The Lion

COMMAND: coop lion, coop lion intro
NEEDS: a co-op save
STATUS: Tested in game on 2026-10-24, on build 24463856

The Lion is a boss cut from the game. Its model, animations and attacks are still in the files, but it has no table row. coop lion adds the 222 rows it needs to the game's tables in memory and spawns it as a real enemy, and coop lion intro plays its entrance first. Nothing is written to a save, and only your game has the Lion.

Gardener and Tendril fights

COMMAND: coop gardener fight, coop tendril fight
NEEDS: a co-op save
STATUS: Not tested in game yet

coop gardener fight and coop tendril fight spawn two more cut Naytibas as enemies, the way coop lion does. The Gardener is an artillery Naytiba about 20 m tall that never walks and shells EVE from its mouth; the mod adds the 13 rows it lacks. The Tendril strikes with four chains on its head; the mod adds 107 rows and builds its attack presentations in memory.

Hairstyles, suits and emotes

COMMAND: coop wear, coop emote <name>
STATUS: Not tested in game yet

coop wear puts EVE in one of two cut hairstyles (mechanical cat ears, rabbit ears) or one of four cut suits, Gothic Rose among them. Your equipment and saves do not change, and your friend sees the look too. coop emote plays 31 photo-mode poses, two waves and six clips made for two enemies that have no character in the game files.

Flight, slow motion and glide

COMMAND: coop fly on, coop slowmo on, coop glide on
NEEDS: a co-op save
STATUS: Not tested in game yet

coop fly on and coop slowmo on turn on the developer flight and slow motion, which the game ships turned off. coop glide on brings back EVE's cut glide: with Jump held in the air, she falls at a tenth of normal gravity.

Scenes, subtitles and developer menus

COMMAND: coop scene, coop lines, coop shortcut, coop devmenu
NEEDS: a co-op save for coop scene and coop devmenu
STATUS: Not tested in game yet

coop scene plays two cut scenes through the game's cutscene player: Emil's farewell from an ending of the first DLC, and Orcal's monologue from the 2022 trailer. coop lines shows the subtitles of four scenes cut before they were voiced. coop shortcut lists the 15 developer saves of the cut Load Shortcut menu, and coop devmenu runs the 20 rows of the developer menu that still work.

TEST PAK

Both need the zMXIII_P test pak, which does not come with the mod. Without it the commands refuse and change nothing.

Matrix XIII

Experimental

COMMAND: coop mxiii, coop mxiii leave
NEEDS: the zMXIII_P test pak, a co-op save, no session
STATUS: Experimental. With test pak v2, the travel reached the dungeon in game after a reload. The rest is not tested in game yet.

Matrix XIII is a dungeon cut before release. The game's tables keep its four zones and their enemies, but no pak holds its map, and no camp or warp leads there. coop mxiii gives its first zone a camp and travels there, and coop mxiii leave brings EVE back out.

Lily's signal

Experimental

NEEDS: the zMXIII_P test pak, a co-op save, no session
STATUS: Experimental. Not tested in game yet.

Two quests of the mod's own, near the end of the story. A short prologue, "A Second Signal", sends EVE to Lily. A longer quest, "On Time", leads through Matrix XIII and back to her. Three talks between EVE and Lily play in the game's own subtitle box.

Left and Right arrowsSwitch tab
Up and Down arrowsMove

STEPS

Close the game before you copy, change or delete any mod file.

Install UE4SS for Stellar Blade, from the package "Stellar Blade UE4SS 1.3".
Download StellarCoop-v0.9.0.zip, unzip it, and copy the StellarCoop folder into SB/Binaries/Win64/ue4ss/Mods/ in the game folder. You should end up with Mods/StellarCoop/Scripts/main.lua, and StellarCoop.dll and enabled.txt next to Scripts/.
Start the game. The mod opens its guide, then asks whether to play on co-op saves: choose Decide later until you have backed up your saves. Load a save and press F6. The screen shows Co-op: not in a session.

To find the game folder: in Steam, right-click Stellar Blade, then Manage, then Browse local files.

Back up your saves before the first session. On Windows they are in %LOCALAPPDATA%\SB\Saved\SaveGames\<your Steam ID>\. Steam Cloud syncs this folder.

Full install guidegithub.com

REQUIREMENTS

GAME: Stellar Blade on Steam (PC), build 26123051, installed by Steam on 2026-11-05
UE4SS: v3.0.1 Beta, as packaged in "Stellar Blade UE4SS 1.3"
SYSTEM: Windows, or Linux with Proton (Steam Deck included)
PLAYING TOGETHER: both players on 0.9.0 and the same game build. Link protocol 19.
CONSOLE: optional. ConsoleEnablerMod, in the same UE4SS package, for the coop commands. F10 or ~ opens it. The keys work without it.
CONTROLLER: XInput (Xbox controllers, the Steam Deck, any controller under Steam Input). A DualSense needs Steam Input turned on for Stellar Blade.

LINUX AND STEAM DECK

Use the same zip. UE4SS starts through the dwmapi.dll next to the game's executable, and Proton can load its own copy instead. UE4SS then never starts and writes no UE4SS.log. If that happens, right-click Stellar Blade in Steam, open Properties, General, and set Launch options to:

WINEDLLOVERRIDES="dwmapi=n,b" %command%

The save folder under Proton is <Steam library>/steamapps/compatdata/3489700/pfx/drive_c/users/steamuser/AppData/Local/SB/Saved/SaveGames/<your Steam ID>/.

From the source code on Linux, python3 tools/install.py runs the tests, builds the DLL with clang-cl and copies the mod. It backs up the files it replaces into ~/StellarCoop-install-backups first.

Left and Right arrowsSwitch tab

VERSION: 0.9.0
RELEASED: 2026-11-09
GAME BUILD: 26123051
PROTOCOL: 19
FILE: StellarCoop-v0.9.0.zip, about 3 MB

0.9.0 is ported to Stellar Blade build 26123051, the Steam update of 2026-11-05 (the Bayonetta collaboration). It does not run on the old build 24463856. On the new build, 0.8.0 turns its native part off, so both players need 0.9.0.

On 2026-11-09, on one PC, 0.9.0 started its native part on build 26123051, switched to the co-op saves and loaded them, and added every table row it needs with none refused. It has not been played between two PCs on this build yet.

The zip holds SHA256SUMS.txt with the SHA-256 sum of every other file in it. StellarCoop.dll is not code-signed, so Windows Defender may quarantine it. Compare its sum with its line in SHA256SUMS.txt, and if they match, restore it from Windows Security, Protection history.

Tip: Co-op saves are copies of your own saves. Your saves stay as they were unless you export a co-op save over one.

QUESTIONS

Does my friend need the mod too?

Yes. Both players need SBO 0.9.0 and Stellar Blade on Steam, build 26123051. Two games with different link protocols cannot link, and the player who tries to join sees Version mismatch.

Is there a server?

No server of our own. The two games link through the Steam client that the game already runs. The host leads the session, and a session holds 2 players.

What happens to my own saves?

Nothing, unless you export a co-op save over one of them, and the mod backs that save up first. Shared enemies, shared quests (experimental, off by default), Night Operation, the challenges, Doro races and most cut-content commands run only on co-op saves: copies of your saves that the mod makes on the title screen, after it backs up every save into StellarCoopBackups. Hosting, joining and your friend's EVE work on any save. Back up the save folder anyway before you play. Steam Cloud syncs the copies like your own saves.

Can someone who is not my Steam friend join?

Yes, with a join code. Set Options > Session > Who can join to With a code, host, and send them the 7-character code. They wait until you select Accept. With no answer in 60 s they are refused, and a refused player cannot come back to that session.

Is the co-op menu in my language?

It uses the game's text language, any of the 23 the game ships. Set Menu language to English in Options (ui_language=english) to keep it in English. The Steam link notices and the logs stay in English.

Is the mod free?

Yes. It is free software under GPL-3.0-or-later, and its source code is on GitHub. It contains no game files and runs on your own copy of the game.

What does the mod leave alone?

It never contacts SHIFT UP's servers: the cut Night Operation matchmaking is blocked, and one of the mod's tests fails if any of its scripts or native code could reach it. It never writes your unlocks or equipment. On a game build it does not support, every feature that reads the game's memory stays off.

Has it been played between two PCs?

Yes, first on 2026-10-17, between a Linux PC with Proton and a Windows PC, at about 240 ms ping. Version 0.9.0 has not: on build 26123051 it has run on one PC only (2026-11-09).

PROBLEMS

F6 does nothing.

Close the game and look in ue4ss/UE4SS.log for lines that start with [StellarCoop]. With none, UE4SS did not start the mod: check that the path is Mods/StellarCoop/Scripts/main.lua, with StellarCoop.dll and enabled.txt next to Scripts/. Windows Extract All can add one folder level. Native part not loaded means that StellarCoop.dll is missing or was quarantined.

Steam updated the game and the mod stopped working.

On another game build, coop status shows engine=off, and every feature that reads the game's memory stays off until an SBO version supports that build. To stop updates in the background, set Stellar Blade's Properties, Updates, Automatic updates to Wait until I launch the game. Steam still installs a waiting update when the game starts.

My friend cannot join.

Version mismatch means different link protocols or game builds: update together. Invite held: joining once your save has loaded. is normal. Could not join: that game is full. means the session already has 2 players.

I do not see my friend's EVE.

She shows only when you are both on the same map. On different maps, a notice says where each of you is. Otherwise, type coop status in the console: it says why.

The game ignores its keys after the co-op menu or the chat.

Open the console (F10 or ~) and type coop ui reset. Without the console, press Ctrl+R or restart the game.

What do I send with a bug report?

Close the game first, because each launch overwrites UE4SS.log. Post coop-report.txt, coop-link.log and coop-link.old.log from Mods/StellarCoop/, and ue4ss/UE4SS.log, on the Discord (discord.gg/tvFApEEVfj). They contain both players' Steam IDs and Steam names, lobby IDs and folder paths, which can show your Windows user name. They hold no passwords.

Left and Right arrowsSwitch tab
Up and Down arrowsMove

Tip: If a save looks wrong, turn Steam Cloud off before you start the game again.

Two additions are being built and are not in any release:

a PvP arena, with matches found through Steam matchmaking;
lobbies built in Eidos 7, where players wait for a match. The pictures on this site are draft renders of these lobbies, taken in the Unreal editor.

There is no release date.