ChatGPT Web returns 404 'Model not found' based on User-Agent, payload reveals 'gpt-6'
Ararararararaki · ghdev · 2026-10-15
- A new openai/codex issue reports every ChatGPT Web message failing with 404 {"detail":"Model not found"} on Chrome 155, Edge 155 and the Codex desktop app, while the same account and conversation works fine on mobile.
- Overriding only the User-Agent to Chrome 148 makes the identical request return 200, indicating UA-based client routing is the culprit.
- Notably, the failing request payload sends model name gpt-6, offering a rare peek at the model's codename.
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