It's also my experience that Claude loves to reimplement the wheel instead of reading code to look for an existing implementation of what it wants to do.
I've been working with Opus 4 on ultrathink quite a bit recently and did some quick tests with Sonnet 4.5, I'm fairly impressed, especially with its speed but I did feel it was a lot less strict with my rules, existing patterns, etc. compared to Opus 4.
Maybe it's better with a better CLAUDE.md structure? I don't use those a lot, just telling Opus to think got 'good enough' results I guess. Not sure.
I hope there's an Opus 4.5 coming out soon too. In the meantime I'll see if I can get to do better with some extra prompting or I'll go back to Opus of if I don't need the speedier responses.
