Claude Fable 5.1

Anthropic released Claude Fable 5.1 on September 1, 2026, alongside Mythos 5.1, a restricted-access version of the same underlying model available to vetted cybersecurity and life-sciences organizations that need capabilities the public release keeps guarded. Fable 5.1 keeps the same $10 per million input and $50 per million output token pricing as Fable 5, but cuts prompt-cache reads from $1.00 to $0.25 per million tokens, a change Anthropic says lowers effective cost by around 25 percent for typical workloads and as much as 45 percent for heavily agentic ones that lean on cached context. Anthropic reported 52.6 percent on Terminal-Bench-Science as one of the headline benchmark gains over the original Fable 5.