I just checked, it has claude available through the API. I asked Claude itself and it said the subscription service is only available through Claude code.

Did you use some kind of plugin? I'd like to use opencode with my Claude subscription.

Thanks for the link, though that particular project is abandonware.

The active project seems to use Claude code's agent API https://github.com/anthropics/claude-agent-sdk-typescript so yes you can issue commands to Claude code from opencode, but the harness in that case is still ultimately Claude code, with all the big fat system prompts that come with it.