GitHub Copilot in vscode has two ways to access Opus: the Copilot harness or the Claude Code Agent SDK within Copilot.

And that's if we assume that the vscode GHCP default Agent ("Local") is the same as the "Copilot CLI" one that is also selectable in vscode. I have not tried that one.

A few weeks ago the Claude Code Agent SDK was much better than the default Copilot Agent, but nowadays I am not sure.

open source harnesses are also improving rapidly.

Some people would claim they are already far better than CC and Codex.

which harnesses, and which when?

Mimocode(opencode), Pi Coding Agent

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).

I’ve only used Opus in GitHub copilot and was hugely underwhelmed. It was barely usable. Are you saying it’s better with the official Anthropic tools?

Night and day in my opinion. But these are all purely Feels so YMMV etc.

I like how especially the Claude Code CLI version communicates how it's progressing, something they hide a lot more on the desktop app for example.

I don't know about better but it's certainly different. It's painfully slow through claude code vscode extension compared to copilot but maybe "smarter", I feel like I have to correct it less using sonnet on both. I don't use opus much because of the cost but coworkers say the difference between harnesses there is also pronounced.