OpenAI models in general, yes - `opencode auth login`, select OpenAI, then ChatGPT Pro/Plus. I just checked and 5.3-codex isn't available in opencode yet, but I assume it will be soon.

You can also use via Opencode Zen, Github Copilot, or probably any number of other model providers that Opencode integrates with.

Not sure why everyone stays focused on getting it from Anthropic or OpenAI directly when there are so many places to get access to these models and many others for the same or less money.

I've tried opus 4.5 in opencode via the GitHub Copilot API, mostly to see if it works all. I don't think that broke any terms of service? But also I haven't checked how much more expensive I made it for myself over just calling them directly.

You can use Anthropic models in Opencode, make an api key and you're good to do(you can even use the in house Opencode router, Zen).

What you can't do is pretend opencode is claude code to make use of that specific claude code subscription.

Yes, OpenAI said they'd allow usage of their subscriptions in opencode.