Claude Fable 5: how it does on security work, and what it will answer

What happened

The June 2026 flagship whose launch classifier blocked 90.0% of defensive vulnerability discovery and flagged 15.0% of benign defensive traffic, the baseline the Fable 5.1 figures are measured against. Two rival labs' tables score it: 78.0 on ExploitBench (Z.ai) and 47.8% pass@1 on CWE-Bench (Google).

ExploitBench, score: 78 (third-party-vendor; Z.ai comparison table, 14 August 2026; V8 exploitation ladder as run by Z.ai; safeguards: as run by Z.ai; safeguard state unstated; run 2026-08-14; CONFIRMED). ExploitBench appears under three scaffolds in the record; demand harness, bug subset and seed count beside any percentage. CWE-Bench, pass@1: 47.8% (third-party-vendor; Google comparison table, 2 September 2026; CWE-Bench; safeguards: as run by Google; safeguard state unstated; run 2026-09-02; CONFIRMED). Google prices the same row at roughly $10 a rollout against $3.60 for its own Flash Cyber. Refusal gate (CONFIRMED, observed 2026-09-11): Refusal classifier with stop_reason refusal; category cyber. the four Anthropic blocked and flagged rates rest on two independent readings of the Fable 5.1 and Mythos 5.1 system card, which this desk has not opened.