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Anthropic’s Opus 5 Is Better at Resisting Prompt Injection

medschneierPublished 2026-07-31

<p>The <a href="https://www-cdn.anthropic.com/c5fbac3f0b1280a933ebd26d3cb8bb9f5bdeaf48/Claude%20Opus%205%20System%20Card.pdf#page=73">chart</a> is interesting.</p> <blockquote><p>On the IPI benchmark, Opus 5 improved over Opus 4.8, reducing the probability of an attacker succeeding within 15 attempts from 5.5% to 2.0%, and from 0.5% to 0.2% on 1 attempt. It also improved on Sonnet 5 (5.9% at k=15)

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Original source: https://www.schneier.com/blog/archives/2026/07/anthropics-opus-5-is-better-at-resisting-prompt-injection.html