Claude Fable 5.1

AnthropicMCP Tool CallReasoning

anthropic/claude-fable-5-1Closed API

Claude model for demanding reasoning and long-horizon agentic work

Benchmark Pricing$10.00 / 1M in$50.00 / 1M out$0.25 cache read

Context: 1,000,000 tokens•Max Output: 128,000 tokens•Knowledge: 2026-06•Released: 2026-09-01

TECHNICAL SPECIFICATIONS

Context Window1,000,0001M tokens

Max Output128,000128K tokens

LicenseProprietaryCloud API only

Input Modalities

TextVisionPDF

Function / Tool CallingSupported (MCP Ready)

Structured OutputsGuaranteed Schema

MODEL CONTEXT PROTOCOL (MCP) READINESS

✓ Claude Fable 5.1 natively supports OpenAI / Anthropic format tool calling and is fully compatible with MCP servers and agent loops.

MCP Context Window Recommendations

With a context capacity of 1,000,000 tokens, this model can handle extremely large MCP resource manifests, complete database schemas, and multiple active server tool definitions simultaneously without degradation.

STANDARDIZED BENCHMARKS & EVALS

Terminal-Bench-Sciencescore

52.6

Terminal-Benchscore

55.8

GDPval-AAElo

1853

OSWorldpartial score

77.9

OSWorldstrict success rate

41.7

Humanity's Last Examscore

60.9

Humanity's Last Examscore

AutomationBenchpass rate

31.4

CursorBenchscore

73.4

API CALL INVOCATION EXAMPLE

// Example: Calling Claude Fable 5.1 via OpenAI SDK
import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.ANTHROPIC_API_KEY,
});

const response = await client.chat.completions.create({
  model: "anthropic/claude-fable-5-1",
  messages: [{ role: "user", content: "Hello! Can you inspect MCP tools?" }],
});

console.log(response.choices[0].message.content);