Copilot Web: Model "gpt-5.3-codex" is not available.

[A-Infor]

Describe the bug

I can't run Copilot to make code as agent for me, because it always provides me this error message:

Copilot Error
Copilot has encountered an unexpected error: [runtime:-32603] Request session.create failed with message: Model "gpt-5.3-codex" is not available.

Affected version

No response

Steps to reproduce the behavior

1. Try to run Copilot from https://github.com/copilot to work as an agent on code writing;
2. Get the error: Model "gpt-5.3-codex" is not available.

Expected behavior

Not get an error. Instead, get code.

Additional context

No response

[A-Infor]

I've found this configuration page: https://github.com/settings/copilot/coding_agent
In that place, I could turn on both Claude and Codex.
This did not fix the issue.

[A-Infor]

I'm Copilot Student. There is no model available at all for Agent?
If there is any, how to switch?