I've tried all of the models available right now, and Claude Opus is by far the most capable.
I had an assertion failure triggered in a fairly complex open-source C library I was using, and Claude Opus not only found the cause, but wrote a self-contained reproduction code I could add to a GitHub issue. And it also added tests for that issue, and fixed the underlying issue.
I am sincerely impressed by the capabilities of Claude Opus. Too bad its usage is so expensive.