Is this about normal system prompt instructions or instructions for the auto mode classifier? I'd be a bit more surprised about the classifier forgetting instructions.
The commenter you replied to mentioned that you can customize the auto mode classifier by providing a prompt, implying that this would be a more robust way of constraining Claude's behavior. It wasn't clear from your response whether you were using this functionality. You might try it out as a way to more reliably prevent these kinds of workarounds.
It's absolutely not reliable, and we have opened a few issues for that.
For example: our instructions (which are read by the model and classifier) include "do not use sed/python/perl/etc, always use the edit tool for editing", and this only gets followed for a few messages. We have introduced scripts to block those ourselves, since the classifier doesn't care.
Because of those problems, my team is currently testing OpenAI after about a year of Anthropic.
