Fix “Codex could not start” in VS Code by downgrading OpenAI.chatgpt

TL;DR: For the Codex VS Code error Codex could not start, the most reported workaround is to install OpenAI.chatgpt@26.1007.21434 instead of 26.1021.22027 and disable auto-update for that extension. This guide is based on user reports and shared logs in openai/codex#56691, not on a maintainer-confirmed root cause.

Applies to: Codex VS Code extension OpenAI.chatgpt, especially 26.1021.22027 on VS Code 1.143.1 for Windows, with similar user reports on Linux. Last checked: 2026-11-03.

Codex could not start

Codex could not start
The extension could not start its user interface.

Codex shows Codex could not start in VS Code when the Codex sidebar webview fails to initialize; the likely version-specific trigger is OpenAI.chatgpt extension 26.1021.22027, because multiple users reported that downgrading to 26.1007.21434 restored the sidebar in the same VS Code environment (reported in openai/codex#56691). This is your case if the Codex icon appears in the VS Code Activity Bar, but selecting the Codex sidebar opens an error panel instead of the Codex UI.

1. Close all VS Code windows.

2. Install the reported working Codex extension version from a terminal that can run the code command:

   code --install-extension OpenAI.chatgpt@26.1007.21434 --force

3. If the code command is not available, use the VS Code UI path reported by users: open Extensions, find Codex or OpenAI.chatgpt, select the gear icon, select Install Specific Version…, then choose 26.1007.21434 (workaround reported in openai/codex#56691).

4. Disable automatic updates for the Codex extension so VS Code does not immediately move the extension back to 26.1021.22027: open Extensions, find Codex or OpenAI.chatgpt, select the gear icon, then choose the extension-level auto-update disable option for that extension (workaround reported in openai/codex#56691).

5. Restart VS Code.

6. Open the Codex sidebar from the Activity Bar.

How to confirm it worked: The Codex sidebar should load its normal interface instead of the Codex could not start panel. In the user reports, the same Windows and Linux installations failed on 26.1021.22027 and loaded normally after installing 26.1007.21434 (reported in openai/codex#56691).

If it still fails: Re-run the install command and confirm the installed extension version is 26.1007.21434, because one reported workaround included disabling auto-update specifically to stop VS Code from returning to 26.1021.22027 (reported in openai/codex#56691). If the version is already pinned and the sidebar still fails, collect the OS, VS Code version, Codex extension version, and any Codex output line containing renderer_ready_timeout, then add those details to the existing GitHub issue or a new openai/codex issue. After the sidebar loads again, use the Codex model-provider setup guide for the next configuration step.

Could not register service worker

Error loading webview provided by 'openai.chatgpt':
Could not register service worker:
InvalidStateError: Failed to register a ServiceWorker:
The document is in an invalid state.

Codex can show Could not register service worker during the same VS Code sidebar startup failure; user logs tied the failure to a Codex webview renderer that did not become ready before a 30-second timeout (reported in openai/codex#56691). This is your case if the visible error names openai.chatgpt, ServiceWorker, InvalidStateError, or a Codex log line like reason=renderer_ready_timeout.

A reported failing log line was:

[CodexWebviewProvider] Webview renderer did not become ready elapsedMs=29999 extensionVersion=26.1021.22027 reason=renderer_ready_timeout receivedWebviewMessage=false role=sidebar stage=renderer timeoutMs=30000

1. Do not spend more time clearing VS Code cache directories as the primary fix for this symptom. The original Windows reporter said the problem persisted after clearing Cache, CachedData, Code Cache, GPUCache, and Service Worker data under %APPDATA%\Code (reported in openai/codex#56691).

2. Install the reported working extension version:

   code --install-extension OpenAI.chatgpt@26.1007.21434 --force

3. Restart VS Code.

4. Open Extensions, find Codex or OpenAI.chatgpt, select the gear icon, and disable automatic updates for that extension so VS Code does not reinstall the failing version family automatically (workaround reported in openai/codex#56691).

5. Open the Codex sidebar again.

How to confirm it worked: The service-worker error should disappear and the Codex sidebar should render. One Linux Mint report reproduced the failure after manually upgrading back to 26.1021.22027, then reinstalled and pinned 26.1007.21434 as the workaround (reported in openai/codex#56691).

If it still fails: Copy the exact service-worker message and any Codex output line that includes renderer_ready_timeout, elapsedMs, extensionVersion, and timeoutMs. Include whether you are using local VS Code or Remote-SSH, because one Windows report said the timeout also reproduced in a VS Code Remote-SSH window with a separate .vscode-server/extensions/openai.chatgpt-26.1021.22027-win32-x64 installation (reported in openai/codex#56691). Use the general error-handling guide to organize the error text, versions, retry result, and logs before filing the report.

Sources

• GitHub issue: openai/codex#56691 — Codex 26.1021.22027 fails to start UI in VS Code 1.143.1 on Windows
• Related GitHub issue listed by the reporter: openai/codex#56617

Docs: Use the general error-handling guide to organize the exact error text, versions, retry results, and logs before you file a report. → general error-handling guide

Related Docs

• Codex model-provider setup
• General error-handling guide