I use Kimi K3, Opus 5, and Fable on a daily basis.

Fable is the only one that reliably one shots complex changes and makes the right design choices. Everything else requires handholding.

I can let Fable loose on a 12+ hour (for AI) task and it will have performed it flawlessly when I come back the next day. K3 and Opus are not like this.

And no, our harness is not the limiting factor here.