Roll out the changes safely for a live game

Last updated on November 6, 2026

Overview

This guide covers a game that is already live with one Steam app, App A, and that you want to extend with a second Steam app, App B, in the same namespace.

Live game: enable the setting last

Enabling Steam multiple apps too early breaks login for live players. Players of a live game already run builds that do not send the App ID. Once you enable the setting, the App ID is mandatory on every request that carries a Steam ticket, and a build that does not send it fails to log in.

Prepare App A and App B first. Enable the setting last. You can release App B only after that.

What happens to your players

Situation	App A players (live)	App B players
The setting is off	Not affected. They keep logging in.	Cannot log in. The namespace accepts only the App ID configured for App A.
You turn the setting on before you update the App A builds	Cannot log in on builds that do not send the App ID. AGS rejects the login request.	Can log in, if App B is in the App ID list.
You update the App A builds, then turn the setting on and add App B	Not affected.	Can log in.

Follow this plan:

• Prepare your live app (App A): Update App A while the setting is still off.
• Prepare your new app (App B): Build App B so it sends its own App ID.
• Turn on Steam multiple apps: Enable the setting, add App B, and release it.
• Verify the impacted features: Check the features that Steam multiple apps impacts.

Development namespaces and builds

This order protects live players. In a development namespace or with development builds, you can turn on Steam multiple apps right away to try it out, because no live players are affected.

Prepare your live app (App A)

While the setting is off, AGS accepts requests with or without the App ID, as long as it matches the configured one. Prepare App A now, so it keeps working when you turn the setting on.

1. Upgrade to the latest AGS SDK. It adds the optional App ID to the Steam login and account linking calls.

   • Unreal Engine SDK and Unreal OSS: Version TBD
   • Unity SDK: Version TBD

2. Make sure your game client sends the App ID of its own Steam app on login and, if you use it, on account linking. A build that sends it on login but not on account linking breaks linking for its players when Steam multiple apps is enabled. See Send the App ID from your game client.

3. If your game server or Extend app unlocks Steam achievements, make sure it sends the App ID in the unlock request. See Sync Steam achievements.

4. Release the updated game client and game server builds of App A.

Prepare your new app (App B)

1. Build App B with the same SDK and the same changes, so it sends the App ID of its own Steam app.
2. You can release App B to players only after you turn on the Steam multiple apps setting. Until then, the namespace accepts only the single App ID configured for App A, so App B players cannot log in because their App ID is different.

Turn on Steam multiple apps

1. Turn on Enable Steam multi app IDs in both the Steam login method and the Steam IAP configuration, and add App B as the second App ID. Keep App A as the first App ID, because the first App ID is the default app, unless you have another reason to make it the second App ID. See Configure the Steam login method and Configure Steam IAP for both apps.
2. Release App B to players.

Verify the impacted features

Verify in your development namespace first

Ideally, verify these features in your development namespace before you switch to your live namespace. A development namespace has no live players, so you can turn on Steam multiple apps there and check each feature without any risk.

After you turn on Steam multiple apps in your live namespace, check the features that it impacts with both App A and App B. When and how you check depends on your release plan, for example before or after you release App B.

Feature	What to check
Set up user authentication	Players of both apps can log in and link a Steam account. A Steam player who launches either app gets the same AGS account.
Set up Steam in-app purchases	Purchases sync, and the player receives the item you expect from your IAP Item Mapping.
Sync Steam achievements	Unlocks sent with the appId appear in the achievements of that app.
Sync Steam lobbies	Players of the same app share one Steam lobby.

DLC sync is not affected, but if you want to verify it as well, do so.

If you find an issue, see Troubleshooting for the potential issues.