Open VSX Gallery transition and proprietary extension compatibility

Direct answer

VSCodium ships with the Open VSX Registry as the default gallery and does not provide a built-in, selective gallery mix that keeps the telemetry-free build while automatically pulling proprietary Marketplace-only extensions. You can install a proprietary extension manually as a .vsix in VSCodium without adding telemetry to the editor itself, but pointing VSCodium back to the Microsoft Marketplace via extensions.gallery.serviceUrl re-introduces connections to Microsoft services and is discouraged by the VSCodium project.

Extensions that target a specific distribution ID or check for an official VS Code build will install in VSCodium but may refuse to activate. The editor does not block installation based on distribution ID; activation and licensing checks are performed by the extension itself.

Confirmed facts

• Open VSX is an open source extension registry that implements the VS Code extension metadata and install protocol. VSCodium and Eclipse Theia use Open VSX by default.
• An extension is only discoverable from Open VSX if its publisher explicitly publishes or mirrors it there. Proprietary extensions distributed solely via the official VS Code Marketplace will not appear in Open VSX search results and cannot be auto-discovered from that gallery.
• VSCodium’s gallery endpoint is determined by product.json. The default build is telemetry-free and points to Open VSX.

Likely explanation

Compatibility is technical rather than functional. A proprietary extension built against the VS Code extension API will generally run in VSCodium if it is installed as a .vsix or from a gallery that hosts it. Licensing, update channels and marketplace authentication remain publisher controlled. Some Microsoft-published extensions check vscode.env.appName / app root and deliberately deactivate on non-official builds such as VSCodium.

Mixing galleries can cause duplicate extension IDs and conflicting update channels. Open VSX and Marketplace have independent review and signing processes; a version available in one may lag or differ from the other.

Steps for this case

1. Verify availability. Search the exact extension ID and publisher on Open VSX and on the official Marketplace. Compare publisher, version and release dates.
2. If the extension exists on Open VSX, install from Open VSX. No gallery change is required.
3. If the extension is Marketplace-only, obtain a .vsix from the vendor if offered, or download the VSIX from the Marketplace manually. Install via Extensions: Install from VSIX in VSCodium and manage updates manually.
4. Test activation in a non-production workspace and verify commands, license prompts and required APIs before changing team-wide settings.

One missing diagnostic detail that changes the recommendation: which specific extension ID and publisher you need. Microsoft-published extensions such as GitHub Copilot have explicit distribution checks and will not activate in VSCodium even from a .vsix, whereas third-party proprietary extensions often work once installed manually.