gpt-5.3-codex fails with 404 when authenticated via OpenAI API key

[iyoda]

Description
When a user authenticates with a standard OpenAI API key via opencode auth login → "Manually enter API Key", gpt-5.3-codex appears as an available model but fails with a 404 error at runtime.
Root Cause
gpt-5.3-codex is only available via the ChatGPT Codex endpoint (chatgpt.com/backend-api/codex/responses), which requires OAuth authentication. It is not listed on the OpenAI API platform.
The codex plugin (src/plugin/codex.ts) rewrites the request URL to the ChatGPT endpoint for OAuth users, but for API key users it returns early without any filtering:
if (auth.type !== "oauth") return {}
This means gpt-5.3-codex (from models.dev) remains in the available model list, but requests go to api.openai.com/v1/responses where the model does not exist → 404.
Note: Other codex models like gpt-5.2-codex are available on the OpenAI API platform and work correctly with API keys.
Steps to Reproduce

1. Run opencode auth login
2. Select OpenAI → "Manually enter API Key"
3. Enter a valid OpenAI API key
4. Select gpt-5.3-codex as the model
5. Send a message → 404 error
   Expected Behavior
   gpt-5.3-codex should not appear as available for API key users, or a clear error should explain that OAuth is required.

[github-actions]

I've searched for potential duplicates and found several related GPT-5.3-Codex issues, but no exact duplicates:

Related (but different issues):

• Responses using GPT-5.3-Codex (from OpenAI Codex) terminate early #12570: Responses using GPT-5.3-Codex terminate early
• xhigh reasoning variant unavailable for GPT-5.3 Codex #12355: xhigh reasoning variant unavailable for GPT-5.3 Codex
• gpt-5.2-codex TypeError: sdk.responses is not a function. (In 'sdk.responses(modelID)', 'sdk.responses' is undefined) #8622: gpt-5.2-codex TypeError with OAuth

This issue appears to be unique regarding the authentication-based availability filtering and 404 error when using API keys with GPT-5.3-Codex.

[github-actions]

No exact duplicates found. This issue appears to be unique regarding the authentication-based model availability filtering for GPT-5.3-Codex with API keys.

[R44VC0RP]

Confirmed — gpt-5.3-codex is OAuth-only and shouldn't be visible for API key users.

Your PR #12837 looks good, filtering it out for non-OAuth users is the right fix. We'll review and merge it.

For now, if you're using an API key, stick with gpt-5.2-codex or other models that are available on the OpenAI API platform.

[iyoda]

Thanks for the confirmation! Sounds good — using gpt-5.2-codex for now.

[felixzieger]

The model is available via API now and works with opencode.

[jomach]

install opencode -> /connect -> Github Copilot -> /models -> GPT-5.2-Codex