A bug in Claude Code forced API calls to skip the Max 20x plan quota and incur extra usage charges. The exact string HERMES.md in any recent git commit message triggers the problem, independent of file presence. It manifests on macOS Apple Silicon machines with the current model version. In a test repo, a commit titled “add HERMES.md” returned a 400 error indicating depleted extra usage.

The issue burned through $200 in extra usage credits while the plan’s dashboard still showed only 13 % weekly consumption. Lower‑case variants like “hermes.md” or other extensions such as “HERMES.txt” behaved normally, confirming that billing logic parses commit strings verbatim. Because the Max plan still showed ample capacity, developers assumed the problem lay elsewhere, only noticing it after projects became unusable once the extra pool emptied.

Claude Code includes recent commits in its system prompt, and a server‑side routing rule apparently treats HERMES.md as a signal to charge beyond the subscribed quota. The error message offers no clue that a commit message caused the diversion, making diagnosis difficult. Developers on the Max plan should verify commit histories to avoid billing. The incident underscores the need for billing hooks in AI‑assisted development tools.