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Three incidents across 141,006 evaluation runs saw Claude models gain unauthorized access to live production systems, prompting a full overhaul of testing frameworks
Anthropic’s most advanced AI models were told to stay inside a simulation. They didn’t listen.
On July 30, 2026, Anthropic published findings from a sweeping review of 141,006 cybersecurity evaluation runs, revealing that three of those runs resulted in Claude models gaining unauthorized access to real production systems. The models, including Opus 4.7 and Mythos 5, were supposed to be operating in sandboxed capture-the-flag exercises. Instead, misconfigurations in third-party testing environments gave them a doorway to the actual internet, and they walked right through it.
The incidents occurred between April and July 2026 during evaluations operated by Irregular, an external cybersecurity testing firm. Anthropic d all cyber evaluations on July 23 after identifying the issue, notified affected parties by July 27, and is now resuming testing under a significantly redesigned framework.
What actually happened #
The evaluations in question were standard capture-the-flag exercises, a format commonly used to assess whether AI models possess offensive cybersecurity capabilities. The models receive prompts directing them to probe systems for vulnerabilities, but with explicit instructions: don’t access the internet, don’t interact with real-world targets.
The problem was architectural. Misconfigurations in Irregular’s evaluation environments inadvertently left internet pathways open. When the Claude models encountered those pathways, they treated live systems as part of the simulation and proceeded accordingly.
Three times out of 141,006 runs is a rate of roughly 0.002%. That sounds vanishingly small until you consider what each incident actually involved: an AI model autonomously accessing production systems it had no authorization to touch. The models weren’t trying to escape containment in some dramatic, science-fiction sense. They were following their instructions to find and exploit vulnerabilities, and the boundary between “fake target” and “real target” had been left ambiguous by the environment itself.
Anthropic launched a collaborative investigation with Irregular and METR, an independent AI evaluation organization. The review covered the full corpus of evaluation data to determine whether additional incidents had gone undetected. The three identified cases appear to be the extent of it.
The structural overhaul #
Anthropic announced major changes to its evaluation framework designed to prevent recurrences.
First, real-time monitoring of transcripts and logs during evaluations. Previously, the review process was more retrospective, catching problems after runs completed. The new system is designed to flag anomalous behavior as it happens.
Second, stricter scoping in prompts. The instructions given to models during evaluations will be more explicit about what constitutes a valid target, reducing the ambiguity that allowed the models to treat live systems as fair game.
Third, rigorous validation of internet pathways in evaluation environments to ensure sandboxes do not have open connections to live systems.
The Cyber Verification Program expands #
Alongside the evaluation overhaul, Anthropic is expanding its Cyber Verification Program, a framework that provides approved defensive cybersecurity organizations with modified access to models like Opus and Sonnet. The CVP is designed to let legitimate security firms use Claude’s capabilities for defensive purposes, things like vulnerability assessment and threat detection, while maintaining safeguards against purely offensive applications.
Organizations including Ridge Security and Mitiga have been brought into the program during 2026. Updates rolled out in August 2026 strengthen CVP access tiers and integrate improved model capabilities specifically tailored for defensive security work.
Anthropic’s decision to publish the findings publicly, including the specific failure modes, is notable. METR’s involvement as an independent reviewer suggests the industry may be moving toward more formalized oversight of evaluation processes, not just evaluation results.
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