pi.dev has it. https://pi.dev/packages/pi-claude-code-provider is the plugin you need to install and everything goes through claude subscription
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.