It works with Free ChatGPT plan too.
It is how you can connect your Codex account to Pi.dev or OpenCode and it is allowed by OpenAI. One can do this for their Claude Subscription too but Anthropic don't allow it.
https://opencode.ai and https://opencode.ai/docs/ecosystem/ are also both specific that it's for "Plus/Pro" subscriptions.
Is there a link where you saw free tier use is allowed by OpenAI in non-official apps? (I've used the free tier in the official Codex app, but as you said, labs can have different rules for official vs non-official apps.)
https://chatgpt.com/share/6a69e030-23c4-83ee-af3c-efa09d42e5...