If you want to experiment with same-harness-different-models Opencode is classically the one to use. After their recent kerfluffle with Anthropic you'll have to use API pricing for opus/sonnet/haiku which makes it kind of a non-starter, but it lets you swap out any number of cloud or local models using e.g. ollama or z.ai or whatever backend provider you like.

I'd rate their coding agent harness as slightly to significantly less capable than claude code, but it also plays better with alternate models.

I have good experience with Mistral Vibe.

OpenCode