We would be doing it now if it wasn't cutting into frontier companies' revenue.

Eg if you use Claude, you probably want fable architecting, a couple of opus under it managing sub project and sonnet doing the actual function code, because fable coding a "run a query and filter the result" is a massive waste of abilities. But their own sub agent downgrade is limited to one level so if you use fable it will never direct sonnet coders.

Claude can be told to run OpenCode or other harnesses via CLI.

I've been doing this myself, all the time. (The ability to get second opinions and code reviews from Sol and other models is priceless.)

There's nothing restricting it to only controlling subagents that are other Claude models like Opus and Sonnet.

Also, I'm not sure that there's a one-level downgrade. Subagents can be pinned to any model:

https://code.claude.com/docs/en/sub-agents

I tell Astra to plan, delegate and check the work of GLM 5.3-flash and Terra medium/high subagents now.

i keep the others in tmux panes and tell the main agent to ask them for their plans and while they run in the background, formulate its plan. Then, when done, review the other plans, and revise as warranted based on other plans.