It's been known for years that prompts which boost performance with one model, can harm performance with a different model. The same goes for harnesses. It looks like they'll need to customize Claude Code's prompts depending on which model is running, for optimal results.

For example if you read the prompts, it's pretty clear that a lot of them are leftovers from the early days when the models had way less common sense than they do now. I think you could probably remove 2/3rds of those over-explained rules now and it would be fine. (In fact you might even expect to see improvement to performance due to decreased prompt noise.)