Yep. That's what I do. Just API keys and you can switch from Opus to GPT especially this week when Opus has been kind of wonky.
Or have Claude write the code and Gemini review it. (Was using GPT for review until the recent Pentagon thing.)
'just API key' lol. just hundreds of dollars at a minimum
I pay $100/mo to Anthropic. Yesterday I coded one small feature via an API key by accident and it cost $6. At this rate, it will cost me $1000/mo to develop with Opus. I might as well code by hand, or switch to the $20 Codex plan, which will probably be more than enough.
I'd rather switch to OpenAI than give up my favorite harness.