Yup I've mentioned this in another thread, I got gpt 5.4xhigh to improve the throughout of a very complex non typical CUDA kernel by 20x. This was through a combination of architecture changes and then do low level optimizations, it did the profiling all by itself. I was extremely impressed.
I was using codex cli with 5.4xhigh. So it was able to iteratively improve from simple prompts on my part (can you give some architectural ideas to improve the performance? And once it does, I just say can you implement and benchmark it).
I think it was a bit like Karpathy's autoresearch, except I was doing manual promoting... Though I feel I could definitely be removed from that equation.
