Codex CLI rejects gpt-5.6 with ChatGPT auth despite availability in ChatGPT apps

What happened?

I have access to the new gpt-5.6 model in ChatGPT on other surfaces, including iOS and Windows, but Codex CLI does not appear to support it when using ChatGPT authentication.

The CLI is current according to codex update, but a direct model probe fails with a 400 response:

ERROR: {"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-5.6' model is not supported when using Codex with a ChatGPT account."}}

This makes it look like model availability is inconsistent between ChatGPT app surfaces and Codex CLI, or that the CLI does not surface the reason/rollout state clearly.

Steps to reproduce

1. Use Codex CLI with ChatGPT auth.
2. Confirm the CLI is current:

codex update

Observed update result:

Resolved version: 0.144.1
Codex CLI 0.144.1 installed successfully.

1. Try to run Codex with gpt-5.6:

codex exec --skip-git-repo-check --ephemeral -m gpt-5.6 --sandbox read-only "Reply with exactly: model-ok"

Expected behavior

If gpt-5.6 is available to the same ChatGPT account in ChatGPT apps, Codex CLI should either:

• allow gpt-5.6 when launched with -m gpt-5.6, or
• clearly explain that Codex has a separate model availability policy/rollout from ChatGPT app surfaces and show which models are currently supported for Codex with ChatGPT auth.

Actual behavior

The CLI starts with the requested model, warns that metadata is missing, then fails:

OpenAI Codex v0.144.1
model: gpt-5.6
provider: openai
approval: on-request
sandbox: read-only
reasoning effort: high

warning: Model metadata for `gpt-5.6` not found. Defaulting to fallback metadata; this can degrade performance and cause issues.
ERROR: {"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-5.6' model is not supported when using Codex with a ChatGPT account."}}

Environment

Codex CLI: 0.144.1
Platform: Linux x86_64
Auth mode: ChatGPT account
Configured model before test: gpt-5.5

codex doctor also reports:

Configuration: model gpt-5.5 · openai
Auth: stored auth mode chatgpt
Updates: cached latest version 0.144.1

Additional context

This may be intentional if Codex model availability lags or differs from ChatGPT app model availability, but the current behavior is confusing because there is no obvious app update available and the CLI updater reports the install is current.