Anthropic’s Fable 5.1 Scores 66 as EFS Replaces No-ZDR Policy

Anthropic’s Fable 5.1 scored 66 on the Artificial Intelligence Index, described as the highest result on the index and ahead of Opus 5 at 63 and Fable at 62. Anthropic says an improved caching system should make ordinary workloads 25% cheaper and long-horizon agentic jobs 45% cheaper; these percentages are company claims rather than independent measurements.

Anthropic is set to replace its no-zero-data-retention policy with Enterprise Frontier Safeguards (EFS). Under the new regime, some data is retained on servers and infrastructure owned by the company, while usage continues to be monitored for hostile activity. The change may have contributed to lower enterprise adoption of Fable, but that connection remains uncertain.