Claude Fable 5.1 and Mythos 5.1 launch with lower cache costs and fewer restrictions

Anthropic has launched Claude Fable 5.1 and Claude Mythos 5.1, just about 3 months after the original Fable 5 release. The update improves speed and benchmark performance while cutting cache read pricing by 75% from the previous $0.25 per million tokens. Since cache reads let Claude reuse previously processed context, the reduction is especially relevant for coding agents and other long running workloads. Anthropic estimates Fable 5.1 is around 25% cheaper than Fable 5 for an average workload, with savings reaching up to 45% for tasks that rely more heavily on cached context.

Fable 5.1 is faster and improves across several coding and terminal benchmarks, scoring 55.8% on Terminal Bench 4.0, up from 42%, 73.4% on CursorBench 3.2.0, up from 70.5%, and 52.6% on Terminal Bench Science, up from 24.7%.

Following criticism of Fable 5's restrictions, Fable 5.1 can now identify software vulnerabilities for defensive research and analysis. Anthropic expects around 60% fewer safeguard interventions during an average Claude Code session. Fable 5.1 is available through Claude, the Claude API, Amazon Web Services, Google Cloud, and Microsoft Azure under the claude-fable-5-1 model ID.