Using ChatGPT Subscriptions With BIGGI

If you already pay for ChatGPT Plus or Pro, you can use that subscription to run OpenAI's top coding models directly inside BIGGI — with no extra API charges beyond your subscription.

Why use your ChatGPT subscription?

  • Flat-rate access to OpenAI models: Your subscription covers usage without pay-as-you-go API costs.
  • OAuth login — no API keys: Click "Sign in to OpenAI Codex," authenticate in your browser, and you're done.
  • Full agentic workflows: Generate, refactor, debug, edit files, and run terminal commands inside BIGGI.
  • Multiple AI modes: Switch between Code, Plan, Debug, and Ask modes for different tasks.

Setup

Open Settings (gear icon) and go to the Providers tab. ChatGPT Plus/Pro uses OAuth authentication — follow the sign-in flow to connect your ChatGPT subscription.

If OpenAI is already connected from an API key, environment variable, or biggi.json config, you can still sign in with ChatGPT from the OpenAI provider row. BIGGI uses the ChatGPT sign-in for Codex models until you disconnect it, then falls back to your existing OpenAI API configuration.

Tips and Notes

  • Subscription Required: You need an active ChatGPT Plus or Pro subscription. This provider won't work with free ChatGPT accounts. Codex is included in ChatGPT Plus, Pro, Business, Edu, and Enterprise plans. See OpenAI's ChatGPT plans for more information.
  • No API Costs: Usage through this provider counts against your ChatGPT subscription, not separately billed API usage.
  • Authentication Errors: If you receive a CSRF or other error when completing OAuth authentication, ensure you do not have another application already listening on port 1455. You can check on Linux and Mac by using lsof -i :1455.
  • Sign Out: Use the Disconnect button in the provider settings.
  • Switching providers: You can switch to Claude, Gemini, or local models at any time — this provider is optional.

Limitations

  • Codex catalog models only. This provider only exposes the models listed in BIGGI's Codex model catalog. It does not give access to every model available through the OpenAI API.
  • OAuth tokens can't be exported with settings. Tokens are stored in VS Code SecretStorage, which isn't included in BIGGI's settings export.

FAQ

Do I need a separate API key? No — just sign in with OAuth using your ChatGPT subscription.

Which ChatGPT plans include Codex access? ChatGPT Plus, Pro, Business, Edu, and Enterprise. Free accounts are not supported.

How is usage billed? Usage counts against your ChatGPT subscription limits — there are no separate API charges.

Can I still switch to other AI providers? Yes. Use OpenAI when it fits and switch to Claude, Gemini, or any local model at any time.