Anthropic released Claude Fable 5.1 and Claude Mythos 5.1. They are the same model with different safeguard levels. Fable 5.1 is generally available. Mythos 5.1 is restricted to trusted access programs. Fable 5.1 costs about 25% less than Fable 5 for typical workloads. Savings reach up to 45% for highly agentic work. Enterprise Frontier Safeguards will give customers full data privacy. EFS will roll out to enterprise customers in phases starting this fall. Mythos 5.1 supports advanced biology and cybersecurity work. Fable 5.1 sets new benchmarks in coding and knowledge tasks. It outperforms Fable 5 across multiple evaluations. Early partners report qualitative improvements in output readability and problem-solving.
What changed
Claude Fable 5 was the prior top model for coding and knowledge work with higher pricing and less precise safeguards.
What it unlocks
Running long, unattended coding and research tasks with higher accuracy and lower cost.
- 25% cheaper than Fable 5 for typical workloads
- up to ~45% cheaper for highly agentic work
- 60% fewer false positives in cybersecurity safeguards
- 52.6% on Terminal-Bench-Science 0.1
What you need to act on it
- usage billed by token
- enterprise plan for EFS
- trusted access program for Mythos 5.1
Sources