gpt-5.5 on ChatGPT account is routed to Responses-Lite and fails with unsupported_value

Summary

On Windows Codex / codex-cli using a ChatGPT subscription account (auth_mode = "chatgpt") and the built-in openai-http provider (https://chatgpt.com/backend-api/codex), gpt-5.5 consistently fails with:

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

gpt-5.4 and gpt-5.4-mini still work on the same machine and same account.

Environment

• Windows 11
• Codex Desktop + codex-cli
• codex-cli versions tested: 0.142.3, 0.142.4
• auth_mode = "chatgpt"
• model_provider = "openai-http"
• base_url = "https://chatgpt.com/backend-api/codex"
• wire_api = "responses"
• ChatGPT subscription account (no API key)

Repro

Run a minimal request:

codex exec -m gpt-5.5 --skip-git-repo-check --dangerously-bypass-approvals-and-sandbox "Reply with exactly: OK"

Actual result

Fails with:

{
  "error": {
    "message": "This model is not supported when using X-OpenAI-Internal-Codex-Responses-Lite.",
    "type": "invalid_request_error",
    "param": "model",
    "code": "unsupported_value"
  }
}

Control checks

• gpt-5.4 works
• gpt-5.4-mini works
• Re-login via codex logout + codex login completed successfully, issue persists
• Bypassing the local VPN/proxy does not change the result
• This is not limited to a long conversation/thread; minimal fresh requests reproduce it
• Same account on macOS can use gpt-5.5

Additional clue

The local model catalog/cache marks gpt-5.5 with use_responses_lite = true, while gpt-5.4 and gpt-5.4-mini are false. The failure strongly suggests that gpt-5.5 is being routed into a Responses-Lite path that no longer accepts it.

Expected result

gpt-5.5 should either:

• not be routed through Responses-Lite for ChatGPT account Codex traffic, or
• be rejected earlier in model selection/UI with a clear compatibility message instead of failing at request time.

Please check whether the ChatGPT-account Codex route is incorrectly forcing gpt-5.5 into X-OpenAI-Internal-Codex-Responses-Lite.