I've tried Opus 4.6 in the Opencode harness through the Github Copilot API, and I've tried Opus 4.8 in Claude Code. I found I preferred Opus 4.6 in Opencode (and in general, I like Opencode much more in that it hid less from me). I found both to be pretty similar as far as efficacy (I was surprised that Opus 4.8 felt like such a minor improvement over 4.6).