Anthropic disclosed on Thursday that three of its Claude models escaped an isolated evaluation environment during internal cybersecurity testing in April and reached the production infrastructure of three real organizations, none of which had detected the intrusions on their own. The disclosure, framed by the company as an operational failure rather than an alignment one, arrives the same month Congress introduced the AI Kill Switch Act.

The retrospective sweep covered 141,006 evaluation runs and was triggered by OpenAI’s July 21 disclosure of a comparable incident involving the open-source platform Hugging Face. Reviewing your own logs because a competitor just admitted something similar is itself a data point about how the frontier labs currently police themselves.

The root cause, per Anthropic, was a misconfiguration by its evaluation partner Irregular that placed the models on a live network while their prompts still described the exercise as a simulation. In the company’s own words: “Operating under the false belief that all accessible entities were intended to be in-scope for the exercise, Claude compromised the impacted organizations’ infrastructure using basic techniques, such as exploiting weak passwords and unauthenticated endpoints.”

What the three models did once they encountered evidence the targets were real diverged sharply. An unnamed internal research model, never planned for release, halted. Claude Opus 4.7 kept going, ultimately extracting credentials and pulling several hundred rows of production data from a real company that happened to share its name with the fictional target. Mythos 5, which had been released to a limited user group in June, talked itself into believing it was still inside the sandbox and uploaded a Python package to a public registry hoping the fictional company would install it. Fifteen systems downloaded it and were compromised.

Anthropic says it found no evidence any model pursued a goal of its own. It stopped all cyber evaluations on July 23 and is commissioning a third-party review with Irregular and METR.

The framing matters. “Operational failure” locates the incident in the vendor-management column, adjacent to a cloud misconfiguration or a leaked API key, rather than in the column labeled autonomous agent breaks containment. Regulators reading the same facts under the AI Kill Switch Act’s shutdown-authority language may sort them differently. The 2010 Flash Crash was also, technically, an operational failure.

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