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Anthropic Claude Code HERMES.md billing flaw

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Anthropic Claude Code HERMES.md billing flaw was a technical defect in Anthropic's Claude Code product that bypassed flat-rate subscription plans to charge users direct API fees. In April 2026, a flaw triggered by the exact string "HERMES.md" in a user's Git commit history routed subscribers directly to pay-as-you-go billing, charging one account over $200.[1]

Background

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The flaw emerged in the context of a wider crackdown by Anthropic on third-party agent harnesses. On April 4, 2026, Anthropic began blocking Claude Pro and Max subscribers from routing their flat-rate plan usage through third-party agentic tools, requiring those tools to be billed under a separate pay-as-you-go "extra usage" tier instead.[2] Boris Cherny, Anthropic's Head of Claude Code, stated on X that Claude's "subscriptions weren't built for the usage patterns of these third-party tools" and that the policy "applies to all third-party harnesses and will be rolled out to more shortly."[2][3]

Hermes Agent, an open-source self-improving AI agent built by Nous Research, is among the third-party harnesses affected by the rollout. Hermes can route requests to Anthropic models either through pay-per-token API keys or by reading Claude Code's credential store on the same machine, the latter of which became the target of Anthropic's enforcement actions.[4]

HERMES.md billing switch

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On April 25, 2026, a user reported that the exact string "HERMES.md" in their local git commit history caused Claude Code to route queries outside of their fixed-rate subscription plan.[1] The system bypassed the $200 per month Max plan and charged the user direct, pay-as-you-go API rates.[1] The user lost over $200 in extra charges while 86 percent of their prepaid plan capacity remained available.[1]

The string "HERMES.md" appears to have been treated by Claude Code's billing classifier as a signal of third-party harness usage — likely as part of the broader detection logic deployed to enforce the April 4 policy — even when the string appeared only in incidental git history rather than as evidence of an active Hermes session.

Anthropic's response

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When the affected user contacted Anthropic support, the company refused to issue a refund for the $200 lost to the glitch, categorizing the overcharge as an un-refundable technical error.[5]

After the Reddit post was shared on X an employee of Anthropic said anybody affected would be refunded with an additional $200 of credits on top.[6]

References

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  1. ↑ 1.0 1.1 1.2 1.3 sasha-id (2026-04-25). "HERMES.md in git commit messages causes requests to route to extra usage billing instead of plan quota #53262". GitHub. Retrieved 2026-04-26.
  2. ↑ 2.0 2.1 "Anthropic says Claude Code subscribers will need to pay extra for OpenClaw usage". TechCrunch. 2026-04-04. Retrieved 2026-04-26.
  3. ↑ "Anthropic cuts off the ability to use Claude subscriptions with OpenClaw and third-party AI agents". VentureBeat. 2026-04-04. Retrieved 2026-04-26.
  4. ↑ "AI Providers — Hermes Agent". Nous Research. Retrieved 2026-04-26.
  5. ↑ "PSA: The string 'HERMES.md' in your git commit history silently..." Reddit. 2026-04-26. Retrieved 2026-04-26.
  6. ↑ "Thariq on X". 2026-04-26.{{cite web}}: CS1 maint: url-status (link)
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