A developer on Anthropic's $200/month Max 20x plan discovered that typing the wrong string in a git commit message cost them $200.98 in unexpected charges. The culprit? The case-sensitive text "HERMES.md" anywhere in recent commit history causes Claude Code to route API requests to paid "extra usage" billing instead of the included plan quota. GitHub user sasha-id documented the bug exhaustively, showing that "hermes.md" (lowercase) works fine, "HERMES.txt" works fine, and even having an actual file named HERMES.md on disk works fine. The trigger is purely the string appearing in commit messages, which Claude Code includes in its system prompt.
Trivially reproducible. Filed as issue #53262 on Anthropic's Claude Code repository.
What makes this painful is the billing response. When sasha-id reported the error and requested a refund, Anthropic support refused. Their exact words: "we are unable to issue compensation for degraded service or technical errors that result in incorrect billing routing." That's Anthropic saying their own billing bug that charged a customer for something they'd already paid for is somehow not worth fixing on the money side. And sasha-id had only used 13% of their weekly plan capacity when the extra charges hit.
Nobody from Anthropic has explained why this specific string triggers a server-side routing path that bypasses plan quota. It looks like a hardcoded flag, maybe a leftover from testing or an internal debug switch that somehow made it to production. The bug only manifests on macOS and only with certain Opus models, suggesting it's tied to specific billing infrastructure. Other users have reported similar billing problems too. One commenter on Hacker News described a $100 double charge from Anthropic's auto-reload system that they had to resolve through a credit card dispute after Anthropic ignored their support requests.
For anyone building agents that use Claude Code or similar tools, this is a blunt reminder to watch your usage limits like a hawk. Content-based billing triggers are not something developers expect. Anthropic's policy of refusing refunds for its own technical errors should make you think twice. The GitHub issue has been closed with cost and bug labels attached, but there's no word yet on an actual fix.