Fable 5.1 is now live in Claude Code and the Claude Platform.
It's priced the same as Fable 5, with 75% cheaper API cache reads. It gets a lot further into a long task before it needs your input, is better at telling you when it's stuck, and its writing style is more natural. https://t.co/1xtB71e3Zw
It’s ahead of both Fable 5 and Opus 5 across our agentic coding and computer use evals.
On Terminal-Bench 4.0 in Claude Code, Fable 5.1 scores 55.8%. Fable 5 scores 42%, and Opus 5 scores 52.3% on the same setup.
Our biggest goal with this upgrade was to deliver increased intelligence while making the model safely accessible. So we’ve taken steps to manage costs while improving safety measures.
To lower costs, we’ve kept pricing the same as Fable 5 while lowering the price of cache reads on usage-based billing. Cache reads on Fable 5.1 are $0.25/MTok, down from $1/MTok on Fable 5.
For builders on the Claude Platform with long horizon workloads, a prompt cache-optimized integration will see significant savings.
In Claude Code, cache reads count at a reduced rate toward subscription usage, which remains unchanged. Long sessions billed at API rates can net out 25%-45% cheaper.
context window — The maximum amount of text a model can consider at once — its working memory for the current conversation or task.
distillation — Training a small, cheap model to imitate a big one's outputs, keeping much of the capability at a fraction of the cost.
AI agent — An AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.
Why it matters
Long AI agentAn AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.Full definition → sessions billed at API rates can run 25-45% cheaper on cache-heavy integrations, and new accounts can no longer edit context windowThe maximum amount of text a model can consider at once — its working memory for the current conversation or task.Full definition → preceding thinking blocks, which breaks some multi-turn message rewriting patterns.
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