macOS: Codex VSIX download is served as “Microsoft.VisualStudio.Services.VSIXPackage”

What version of the Codex App are you using (From “About Codex” dialog)?

Not using the Codex desktop app. Using the VS Code extension openai.chatgpt v26.727.40816 on macOS Apple Silicon.

What subscription do you have?

GO

What platform is your computer?

Darwin 25.6.0 arm64 arm

What issue are you seeing?

On macOS Apple Silicon, VS Code failed to install/open the Codex extension from the Marketplace. The extension page showed “Failed to fetch” and the download was saved with the confusing filename Microsoft.VisualStudio.Services.VSIXPackage rather than a normal .vsix filename.

Environment:

• macOS: Darwin 25.6.0 arm64 arm
• VS Code: latest version
• Extension: openai.chatgpt / Codex – OpenAI’s coding agent
• Extension version: 26.727.40816

Full error:

2026-08-03 21:15:59.898 [error] [Network] #46: https://openai.gallery.vsassets.io/_apis/public/gallery/publisher/openai/extension/chatgpt/26.727.40816/assetbyname/Microsoft.VisualStudio.Code.Manifest?targetPlatform=darwin-arm64 - error GET Failed to fetch

2026-08-03 21:15:59.898 [error] [Window] TypeError: Failed to fetch
    at _in (vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:5370:51993)
    at vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:5370:53289)

No VPN, proxy, ad blocker, or custom DNS is enabled. The extension was eventually installed manually, but the normal Marketplace installation flow should work on macOS without requiring users to handle or rename an internally named VSIX package.

What steps can reproduce the bug?

Steps to reproduce:

1. Use a Mac with Apple Silicon and the latest stable version of Visual Studio Code.
2. Open the Extensions view.
3. Search for “Codex – OpenAI’s coding agent” (openai.chatgpt).
4. Open the extension page and click Install.
5. VS Code attempts to fetch the manifest for targetPlatform=darwin-arm64.
6. The request fails with TypeError: Failed to fetch.
7. If downloading the extension package manually, it is delivered with the filename Microsoft.VisualStudio.Services.VSIXPackage, which is confusing and does not have the expected .vsix extension.

Expected result:

The Codex extension installs directly from the VS Code Marketplace on macOS Apple Silicon.

Actual result:

The Marketplace installation fails with “Failed to fetch,” and the manual download flow exposes an internally named VSIX package.

No code snippet, session ID, token usage, or context-window usage applies; this is an extension installation issue.

What is the expected behavior?

Expected behavior:

On macOS Apple Silicon, selecting Install for “Codex – OpenAI’s coding agent” in the VS Code Marketplace should download and install the extension successfully without errors.

If a manual download is provided, it should have a clear .vsix filename, such as openai.chatgpt-darwin-arm64.vsix, and be installable through “Extensions: Install from VSIX…” without renaming or troubleshooting.

Additional information

Additional information:

The problem affects the initial onboarding flow for users who want to use Codex in VS Code. The error suggests a network issue, but no VPN, proxy, ad blocker, or custom DNS was enabled.

The extension package itself appears valid once manually handled, so the issue seems to be in the Marketplace fetch/download and package naming experience rather than the user’s ChatGPT subscription or account.

This issue was observed on August 3, 2026.