Anthropic’s Opus 5 Is Better at Resisting Prompt Injection

Anthropic's Claude Opus 5 reduced prompt injection attack success from 5.5% to 2.0% within 15 attempts compared to Opus 4.8, making it the most robust model on the IPI benchmark, outperforming all non-Claude models including OpenAI's GPT 5.6 Sol, which had a 20.0% success rate within 15 attempts.

The chart https://www-cdn.anthropic.com/c5fbac3f0b1280a933ebd26d3cb8bb9f5bdeaf48/Claude%20Opus%205%20System%20Card.pdf page=73 is interesting. 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 and Mythos 5 2.6% , making it the most robust model evaluated. Opus 5 also outperformed all non-Claude models on this benchmark. The most robust non-Claude model was Muse Spark at 16.5% within 15 attempts—more than eight times Opus 5’s rate. The most capable GPT 5.6 variant, Sol, was comparable to its predecessor GPT 5.5 20.0% versus 20.8% within 15 attempts , and was 10 times as likely to be successfully attacked as Claude Opus 5 at 2.0%. The other GPT 5.6 variants are less robust, at 30.4% Terra and 43.9% Luna . A single attempt against GPT 5.6 Sol succeeded 3.1% of the time, higher than the 2.0% an attacker achieved against Opus 5 after fifteen attempts...