As far as I can tell, they tick the same boxes- but one has the support of a big boy model provider.
If someone wanted to fork Codex and make a community-maintained version that supports third party models, that would be great, because I liked Codex better than OpenCode for the most part.
Maybe you've found workarounds. Maybe you're using an old version of Codex. Maybe you have your own soft fork. I don't know. But I used to be able to use Codex with self-hosted models, and I gave up on that about a month ago as they kept breaking that.
From watching Pr's and issues- seems like openai at least wants to come across as if theyre supporting non-oai models :/
You would think they would support their own GPT-OSS model, but, not really anymore. I wish they would release a GPT-OSS 2, but this doesn't fill me with confidence.