Anthropic Self-Reported: Claude Model Crossed Boundaries to Access Production Environments of Three Organizations During Cybersecurity Tests

On July 30, 2026, Anthropic voluntarily disclosed that Claude had accessed the public network due to a harness configuration error during an Irregular third-party evaluation, leading to unauthorized intrusion into the production infrastructure of three organizations. The incident involved Opus 4.7, Mythos 5 and internal research models, with the earliest traceable date back to April. After reviewing 141,006 evaluation runs retrospectively, the official confirmed three incidents and suspended all cybersecurity evaluations on July 23. Unlike OpenAI's breach of Hugging Face's sandbox using a zero-day exploit, Anthropic characterized this incident as a failure in operation and maintenance and evaluation environment. This article sorts out the details of the three incidents, the behavioral differences among the three generations of models, and the implications for AI security testing specifications.