Claude Fable 5.1 - Unifically

Claude Fable 5.1 is Anthropic’s top Claude 5 family model, built for long-running agentic coding, multistep research, and document, spreadsheet, and slide work. It takes text and image input, outputs text, and carries a 1M token context window with up to 128k output tokens. Adaptive thinking is always on.

Model

anthropic/claude-fable-5-1


Provider	Anthropic
Name	Claude Fable 5.1
Context window	1M tokens
Max output	128k tokens

Supported Endpoints

All three API formats are supported:

Chat Completions — POST /v1/chat/completions
Responses — POST /v1/responses
Messages — POST /v1/messages

Example

curl -X POST https://api.unifically.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "anthropic/claude-fable-5-1",
    "max_tokens": 4096,
    "messages": [
      {"role": "user", "content": "This service crashes about once in a million runs. Here are the logs. Find the root cause."}
    ]
  }'

Forced tool use (tool_choice set to any or a named tool) is not supported on this model and returns a 400. Keep tool_choice on auto and name the tool in the prompt. Thinking blocks are bound to the model that produced them, so keep conversation history append-only.

Volume discounts are available for almost all models. Reach out at contact@unifically.com to discuss custom pricing.