Complete anecdata, but the one thing that was very obvious that something had changed last month was the number of times Claude Code would fail to respect guidelines or blatantly ignore rules clearly laid out in the CLAUDE.md file. This problem was occurring long before the "Context Window" had been filled to capacity as well.

It got to the point where I actually added a line to the top of the CLAUDE.md file as follows:

  To verify that you have read and understood these guidelines, please output the following text "CLAUDE.MD HAS BEEN ACKNOWLEDGED". 

Just to get a sense of whether it was failing to ingest it.