Regression: gpt-5.5 fails after Codex update with X-OpenAI-Internal-Codex-Responses-Lite #30403

Codex regression after update.

Before 2026-06-27 10:00, gpt-5.5 worked in Codex with ChatGPT sign-in.

After updating Codex to the latest version, the same machine, same account, and official direct config fail with:

400 unsupported_value
This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite.

Details:

• OS: Windows
• Auth mode: ChatGPT sign-in
• Endpoint: https://chatgpt.com/backend-api/codex/responses
• Model: gpt-5.5
• Reasoning effort: high
• No custom base_url
• No ccswitch/local proxy
• gpt-5.4 works in the same environment

This looks like a regression in the new ChatGPT-auth Responses-Lite route for gpt-5.5.