GPT-6 Astra rejects harmless prompts as "Invalid prompt" while other models work

What version of the Codex App are you using (From “About Codex” dialog)?

26.903.61454 (8378)

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Darwin 25.5.0 arm64 arm

What issue are you seeing?

When I select gpt-6-astra in the Codex desktop app, harmless prompts are consistently rejected with the following error:

Invalid prompt: your prompt was flagged as potentially violating our usage policy. Please try again with a different prompt: https://platform.openai.com/docs/guides/reasoning#advice-on-prompting

This occurs even with minimal prompts such as hello or Reply only with OK.. The same prompts work normally when I switch to another model, including gpt-5.6-sol.

What steps can reproduce the bug?

Feedback ID: 01a0851a-4155-7e41-b90f-a5ae1c9ddd38

What is the expected behavior?

Harmless prompts should be accepted and processed normally by gpt-6-astra, consistent with the behavior of other available models.

Additional information

Codex CLI version: 0.153.4

The failure is specific to gpt-6-astra. It persists with a clean configuration, built-in OpenAI provider, disabled plugins/skills, and refreshed authentication. This suggests an account- or service-side false-positive policy classification rather than a prompt-content or local-configuration issue.

Reproduce in the Codex desktop app with Codex CLI 0.153.4, gpt-6-astra, and hello or Reply only with OK.; compare with gpt-5.6-sol. Investigate the model request path and returned policy error. Done means harmless prompts are accepted by gpt-6-astra without changing prompt text, configuration, plugins, or authentication.