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Boris Cherny: 'Opus 5 Is Our Least Prompt Injectable Model Yet' — Willison Points to Page 73 of the System Card
Willison highlighted a claim from Anthropic's Boris Cherny on July 25 that Claude Opus 5 is the company's most injection-resistant model to date, performing strongly across prompt-injection evaluations and red-teaming, with the underlying data on page 73 of the Opus 5 System Card. Coming from Willison — who has spent two years arguing that no one has solved prompt injection — the decision to surface it rather than dismiss it is itself the signal. For anyone building agents with tool access, this is the first frontier-model release where the injection numbers are being cited as a differentiator rather than buried.
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