I find it surprising. The piece of code I'm working on is about 10k LoC to define the basic structures and functionality and I found Claude Code would systematically spend significant time and tokens exploring it to add even basic functionality. Part of the issue is this deals with a problem domain LLMs don't seem to be very well trained on, so they have to take it all in, they don't seem to know what to look for in advance.

I went through a couple of iterations of the CLAUDE.md file, first describing the problem domain and library intent (that helped target search better as it had keywords to go by; note a domain-trained human would know these in advance from the three words that comprise the library folder name) and finally adding a concise per-function doc of all the most frequently used bits. I find I can launch CC on a simple task now, without it spending minutes reading the codebase before getting started.