Claude Fable 5.1
Anthropic’s most capable model, built for work that runs for hours and checks its own results.
About Claude Fable 5.1
Fable 5.1 sits above Opus in Anthropic’s lineup. It is the model for jobs that take a long time and many steps: an agent that plans, uses tools across several applications, recovers when something breaks and checks its own work before it reports back. Anthropic’s numbers show where the jump is — 55.8% on Terminal-Bench 4.0, up from 42.0% for Fable 5, and 65.0% on Humanity’s Last Exam with tools.
It always thinks before it answers. You choose how hard, from low to max effort, and the default is high. That makes it the slowest model Anthropic sells, so it earns its place on problems a cheaper model gets wrong, not on everyday drafting.
Where it’s strong
Long-running coding agents that work through a large change on their own.
Research that has to verify its own findings before it reports.
Building finished documents, spreadsheets and slide decks from a brief.
The hardest reasoning problems, where Opus still falls short.
Where to be careful
Slow. Anthropic rates it the slowest model in its current lineup, so it is a poor fit for anything a person sits waiting on.
Requests touching cybersecurity or biology can trip Anthropic’s safety filters and be refused or handed to an older model.
Check whether Opus 5.5 or Sonnet 5.5 already does the job first. For most work, they do.
Price
For scale: 1,000 requests of about 3,000 tokens in and 1,000 out cost $92.00 — a long prompt and a page of answer each. Every rate is published and stays the same from one request to the next. See every model.
Specs
claude-fable-5-1Call it
Use the OpenAI SDK you already have — point it at Roar AI and name the model. Read the docs.
from openai import OpenAI
client = OpenAI(base_url="https://api.roar-ai.com/v1", api_key="roar_live_…")
reply = client.chat.completions.create(
model="claude-fable-5-1",
messages=[{"role": "user", "content": "Summarise this contract in plain English."}],
)Compare Claude Fable 5.1
Questions
How much does Claude Fable 5.1 cost?
Input is $11.50 per 1M tokens; output is $57.50 per 1M tokens. For scale, 1,000 requests of about 3,000 tokens in and 1,000 out cost $92.00. The rate is published and does not change from one request to the next.
Can I use Claude Fable 5.1 alongside other models?
Yes. Every model on Roar AI is on the same API key and the same monthly invoice, so switching from Claude Fable 5.1 to another model is a change to one word in your code.
Is Claude Fable 5.1 open source?
No. Anthropic does not publish the weights, so it is only available through an API like this one.