And what tooling do you use with that? In my experience, there is quite a bit of difference between using, say, OpenCode, or the commercial offerings.

No tooling, just manual use. When doing these comparisons I gather and format all the data they need to figure out the problem, and paste the same thing into all models so it's a pretty even eval.

I doubt Kimi would do well with most harnesses, its outputs are pretty chaotic in terms of formatting but the inteligence is definitely there.