I don't think there's any open models at the moment that can handle the more challenging stuff.

The things that I use Opus for at work is finding bugs in about ~200k lines of microservices and libraries in a niche language. So, we will get these bug reports that are missing context, can't easily be reproduced on our dev server, and are usually the result of something deep in multiple services/libraries combining with very custom configs. I can ask Opus (max thinking) to find what could cause the bug, and it usually nails it in a few hours (would take me 1-2 weeks to trace it myself). The end result will be like less than 10 lines of code to fix it, some tests to reproduce the bug and a nice report explaining it, so it can be checked in an hour or two.