Including the case-sensitive string HERMES.md in git commit messages causes Claude Code to route API requests to "extra usage" billing instead of the plan's quota. This misrouting can lead to unexpected charges, as demonstrated by a $200 increase in extra usage credits while remaining within the Max 20x plan capacity.

A €54,000+ charge occurred within 13 hours after enabling Firebase AI Logic on a Firebase project. The spike in billing was attributed to the use of a Firebase browser key without API restrictions for Gemini requests.