I recently encountered a similar issue when trying to use o1 after a web search. While not ideal, you can use the same workaround for your issue as well:
Try manually setting the model query parameter to o3-mini in the page URL.
For example,
- If your chat URL is
https://chatgpt.com/c/abcdefghijklmnop - Add the query param:
https://chatgpt.com/c/abcdefghijklmnop?model=o3-mini
After the page loads, the o3 model you specified should be selected and usable (but still greyed out in the model selector).
I’m not sure if this workaround has any unintended consequences yet. For now I just assume it doesn’t.