OpenAI's Codex tool is not limited to only calling their models. You can create a profile that uses any OpenAI API compatible endpoint.

It's written in Rust. It seems to perform well. It also seems (from my poking around in it) on the whole well and deliberately written. It doesn't consume memory like a mf'er like Claude Code. It doesn't sit and chew background CPU like I've seen opencode.

I suspect it will accumulate more specific-to-OpenAI-isms over time though.