Anthropic: Claude Fable 5.1

anthropic/claude-fable-5.1

Claude Fable 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work: long code refactors, front-end and visual co...

visiontools

MODALITIES

→

INPUT PRICE

$2per 1M

OUTPUT PRICE

$10per 1M

CONTEXT

RELEASED

Sep 2, 2026

Provider				Cache	Uptime	Chat
ccapi	5.00(1)	$2	$10	Hit rate90.5% Cache read$0.2
Transparent Compute for Agent-Scale Throughput	—	$5	$25	Cache read$0.5

Capabilities

Input modalities

fileimagetext

Output modalities

text

Features

include_reasoningmax_completion_tokensmax_tokensreasoningreasoning_effortresponse_formatstopstructured_outputstoolsverbosity

Get API Key

Create an API key from the Keys page, then set it as an environment variable:

export ONLIST_API_KEY=sk-...

Make your first request

Endpoints

POSThttps://onlist.io/v1/chat/completions

OpenAI Chat Completions format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:anthropic/claude-fable-5.1

POSThttps://onlist.io/v1/responses

OpenAI Responses format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:anthropic/claude-fable-5.1

POSThttps://onlist.io/v1/messages

Anthropic Messages format

Request Headers

Authorization:Bearer $ONLIST_API_KEY

Content-Type:application/json

Model:anthropic/claude-fable-5.1

Code samples

curl https://onlist.io/v1/chat/completions \
  -H "Authorization: Bearer $ONLIST_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "model": "anthropic/claude-fable-5.1",
       "messages": [
         {
           "role": "user",
           "content": "Explain quantum entanglement in one paragraph."
         }
       ]
     }'

Replace $ONLIST_API_KEY with the API key from your Keys page.

Authentication

All requests must include an Authorization: Bearer <TOKEN> header. Generate keys from the Keys page; keys can be scoped to specific models, groups, IP ranges, and rate limits.

Enable streaming

Add "stream": true to receive partial responses as server-sent events in real time.

Streaming example

curl https://onlist.io/v1/chat/completions \
  -H "Authorization: Bearer $ONLIST_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
       "model": "anthropic/claude-fable-5.1",
       "messages": [
         {
           "role": "user",
           "content": "Write a haiku about recursion."
         }
       ],
       "stream": true
     }'

Supported parameters

Name	Type	Description
`include_reasoning`
`max_completion_tokens`	integer	Upper bound on tokens generated, including visible and reasoning tokens.
`max_tokens`	integer	Maximum number of tokens to generate in the completion.
`reasoning`
`reasoning_effort`	string	Constrains effort on reasoning. Supported values: "low", "medium", "high".
`response_format`	object	Specifies the output format. Use {"type": "json_object"} for JSON mode.
`stop`	string \| array	Up to 4 sequences where the API will stop generating tokens.
`structured_outputs`
`tools`	array	A list of tools the model may call. Currently supports functions.
`verbosity`

These are the request parameters this model accepts. Parameter semantics follow the OpenAI Chat Completions specification.