Here's a stress test of sorts that I've had it working on the last couple of days: We have a C -> microcode compiler written in C. I gave it the docs for that compiler and asked it to implement it in OCaml (since it's not very common, but also is a good implementation language for compilers). It can use the first compiler as a golden to compare against. On the frontend it's C language parser -> AST -> IR -> microcode. It's basically at the point now where the original compiler has been. Not only does this generate microcode it also has to generate some Verilog code that loads and runs the microcode. I asked it to come up with some new optimizations that the original compiler doesn't have and it came up with a couple that in some cases reduce microcode lines by 30% (less microcode in this machine means more performant). These are ideas that Claude didn't come up with when it was working on the original compiler (and I recall prompting it several times asking it if there might be other optimizations we could perform).

So all in all, I put it at Opus 4.8 level, at least. And in some ways it's exceeding 4.8.