Anthropic’s Opus 5 Is Better at Resisting Prompt Injection
Brief
The chart 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.