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HERMES.md: Anthropic bug causes $200 extra charge, refuses refund

Summary

When a git repository's recent commit history contains the case-sensitive string HERMES.md, Claude Code routes API requests to "extra usage" billing instead of the included Max plan quota. This silently burned through $200 in extra usage credits while my Max 20x plan capacity remained largely untouched (13% weekly usage).

Environment

  • Claude Code v2.1.119
  • macOS (Apple Silicon)
  • Max 20x plan ($200/month)
  • Model: claude-opus-4-6[1m] (also reproduces with claude-opus-4-7)

Reproduction

Minimal reproduction — no project files needed:

# This FAILS with "out of extra usage" (routes to extra usage billing)
mkdir /tmp/test-fail && cd /tmp/test-fail
git init && echo test > test.txt && git add . && git commit -m "add HERMES.md"
claude -p "say hello" --model "claude-opus-4-6[1m]"
# => API Error: 400 "You're out of extra usage..."

# This WORKS (routes to plan quota)
mkdir /tmp/test-pass && cd /tmp/test-pass
git init && echo test > test.txt && git add . && git commit -m "add hermes.md"
claude -p "say hello" --model "claude-opus-4-6[1m]"
# => "Hello!"

# Cleanup
rm -rf /tmp/test-fail /tmp/test-pass

The trigger is the string HERMES.md in git commit messages — not the presence of a file with that name on disk. Claude Code includes recent commits in its system prompt, and something server-side routes the request differently when this string is present.

What triggers it vs. what doesn't

Commit message Result
"HERMES.md" Fails — routes to extra usage
"test HERMES.md test" Fails
"hermes.md" (lowercase) Works
"HERMES" (no extension) Works
"HERMES.txt" Works
"AGENTS.md" Works
"README.md" Works
File named HERMES.md on disk, clean commit msg Works
Same repo, orphan branch (no history) Works

Impact

  • $200.98 in extra usage credits consumed for requests that should have been covered by the included Max 20x plan quota
  • Multiple projects became completely unusable once extra usage was depleted, while the plan dashboard showed 86%+ remaining weekly capacity
  • The error message ("out of extra usage") gives no indication that content-based routing is the cause, making this extremely difficult to diagnose
  • Any user with HERMES.md in recent git commits would silently have their usage billed to extra credits

Expected behavior

API request billing should not depend on the content of git commit messages in the system prompt. All requests from a Max plan subscriber should route to the included plan quota first.

How I found this

Systematic binary search: cloning affected repos, testing orphan branches, then isolating individual commit message strings until HERMES.md was identified as the exact trigger.