Advanced reasoning

Claude Fable 5.1 API

Our most capable model for complex, multi-step work where quality matters most.

Try in chat Open playground

1M context
131K max output
All plans

Specifications

Model ID: claude-fable-5-1
Context window: 1M tokens
Max output: 131K tokens
Availability: All plans
Released: Sep 2026

Streaming
Reasoning
Vision
Tool use
JSON mode

Pricing

Input / 1M: $0.50
Cached input / 1M: $0.010
Output / 1M: $1.90

A request with 10,000 input tokens and 1,000 output tokens costs $0.0069. Repeated prompt prefixes are billed at the cached rate.

Paid from a prepaid balance. See pricing, the cost calculator and price comparison.

API

Call Claude Fable 5.1

The same key works in both request formats. API access unlocks after your first purchase.

OpenAI format

POST /v1/chat/completions

curl https://api.claudech.com/v1/chat/completions \
  -H "Authorization: Bearer $CLAUDECH_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

Anthropic format

POST /v1/messages

curl https://api.claudech.com/v1/messages \
  -H "x-api-key: $CLAUDECH_API_KEY" \
  -H "anthropic-version: 2026-10-04" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Hello"}]
  }'