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Claude Fable 5.1 API

Access Anthropic Claude Fable 5.1—also searched as Fable 5.1— through EvoLink's unified chat API. Test long-context coding, tool use, prompt caching before integrating.

AnthropicText GenerationAvailable
From $9.500 / 1M input tokens$10.000 official price-5%
API docs
Adaptive thinkingText + image inputPrompt cachingWeb search tool
Production routeLive
Context
1M context · 128K max output
Best For
The hardest repository-scale coding, longest agent runs, judgment-heavy review
Input
Text + images
Output
Text · JSON (structured output) · tool calls
ModelsPricingReadmeAPI

Choose Claude Fable 5.1

Anthropic’s latest Fable model for demanding reasoning, long-horizon agents, and judgment-heavy review. Five billing dimensions — input, cache write, cache read, output, and the web search tool — are metered separately.

Claude Fable 5.1

Anthropic’s latest Fable model

Selected
Model ID
claude-fable-5-1
Best for

Repository-scale software engineering, long-horizon agent runs with heavy tool use, high-stakes code review, and research or analysis work where a wrong answer costs more than a premium token rate.

Input
$9.500 / 1M-5%
646 cr / 1M$10.000official price
Cache write
$11.875 / 1M-5%
807.5 cr / 1M$12.500official price
Cache read
$0.239 / 1M-5%
16.2 cr / 1M$0.250official price
Output
$47.500 / 1M-5%
3230 cr / 1M$50.000official price

All rates are per 1M tokens, shown in USD and credits, and reflect your account's current pricing.

Claude Fable 5.1 pricing

Estimate what one Claude Fable 5.1 request costs before you integrate. The calculator uses your account's current rates, with official pricing as a reference.

Request calculator

Enter the token mix for one request and the number of successful tool calls.

Estimated request cost

Claude Fable 5.1
USD$0.024
Credits1.6183

Official estimate $0.026 · save $0.0013 (5%)

Input tokens0.646 cr
Cache write tokens0 cr
Cache read tokens0.0033 cr
Output tokens0.969 cr

Minimum charge: 0.02 credits per request.

Budget guide

Approximate requests using the current token mix.
Add credits
$10
About 420 requests

For quick testing

$50
About 2100 requests

For regular development

$100
About 4201 requests

For production evaluation

Server-side tool rates

Only successful server-side calls are billed per call; failed attempts have no tool fee, but tokens still apply.
  • Web search$0.010/ call0.68 cr / call

Claude Fable 5.1 API for the hardest coding and agent work

Call Anthropic’s latest Fable model for demanding reasoning and long-horizon agentic work through EvoLink’s unified API at $9.500 / $47.500 per million input / output tokens. Includes a 1,000,000-token context window, 128K max output, prompt caching with separate write and read rates, and the per-search web search tool.

Claude Fable 5.1 is served on EvoLink under the model ID claude-fable-5-1 through Chat Completions · Anthropic Messages, with the same API key and balance you use for every other model. It offers a 1M context window and up to 128K output tokens, plus long-context coding, tool use, prompt caching.

Claude Fable 5.1

Claude Fable 5.1 specs and capabilities

Numbers come from the EvoLink route configuration; capabilities are what the API exposes today.

Context window
1M tokens
Max output
128K tokens
Input
Text + images
Output
Text · JSON (structured output) · tool calls
Reasoning
Thinking mode (on by default)
Tool use
Function calling with multi-step tool sequences
Prompt caching
Cache write + cache read rates
Server-side tools
Web search, billed per successful call
Protocols
Chat Completions · Anthropic Messages
Model ID
claude-fable-5-1

Where Claude Fable 5.1 earns its premium rate

Top-tier pricing only pays off when a task is hard enough that a better answer removes work downstream. Route to Fable 5.1 by the cost of being wrong, not by the cost per token.

Repository-scale software engineering

Inspect large codebases, trace dependencies across services, and plan multi-file changes while holding architectural constraints in one context. Measure accepted patches and review time rather than isolated snippet quality.

Long-horizon agents with heavy tool use

Multi-step orchestration, tool selection, and code execution over long runs, where a single wrong branch costs far more than the token difference. Replay complete assistant messages, tool-call IDs, arguments, and tool results across turns.

High-stakes review and analysis

Security review, migration planning, contract and research analysis, and anything where a confident wrong answer is expensive. The 1M-token window keeps the full evidence set in one place.

When another route is the better choice

Everyday coding, high-volume agents, classification, and latency-sensitive chat usually belong on Claude Sonnet 5. Compare Claude Opus 5’s current token rates and answer quality before choosing it as the default flagship route.

Two ways to use Claude Fable 5.1: EvoLink API or Agent

Use the EvoLink API for product backends and batch jobs, or call Claude Fable 5.1 from Codex, Claude, or Gemini for coding and analysis workflows. Both paths share the same EvoLink API key, balance, model ID, and request history.

Option 1

Integrate with the EvoLink API

Best for: product backends, batch jobs, automated pipelines

Send OpenAI-compatible Chat Completions (or Anthropic Messages) requests to EvoLink and control the model ID, system prompt, output budget, tools, and structured output.

  1. 1Create an EvoLink API key in the console
  2. 2Point your OpenAI or Anthropic SDK at the EvoLink base URL and select the model ID shown above
  3. 3Send one representative request and read the usage field for input, cached, and output tokens
  4. 4Set max_tokens and retries per task; keep tool-call IDs and results across turns
Create EvoLink API Key
Option 2

Call it with an Agent

Best for: coding, review, and analysis tasks in Codex, Claude, and Gemini

Give the Agent the task, the inputs to include, and the acceptance criteria. It assembles the request, calls Claude Fable 5.1 through EvoLink, and returns the answer with token usage.

  1. 1Set EVOLINK_API_KEY in your local environment; never put it in code or a prompt
  2. 2Describe the task, the inputs to include, and the expected output format
  3. 3Ask the Agent to call Claude Fable 5.1 through EvoLink and show the request before sending
  4. 4Let the Agent report the answer, token usage, and any error body

Claude Fable 5.1 API code example and error handling

This example shows the shortest runnable request: an OpenAI-compatible Chat Completions call with a system prompt, a user message, and an output budget. Open the API tab for the complete parameter and response reference.

View complete API docs
cURL
curl -X POST https://api.evolink.ai/v1/chat/completions \
  -H "Authorization: Bearer $EVOLINK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "messages": [
      { "role": "system", "content": "You are a senior engineer reviewing a pull request." },
      { "role": "user", "content": "Review this diff and list the blocking issues with file and line:\n<diff>" }
    ],
    "max_tokens": 8192,
    "temperature": 0.2
  }'

# Anthropic Messages is also available at /v1/messages with the same model
# ID.
# The response includes choices[0].message and a usage object
# (prompt_tokens, completion_tokens, and cache read / write tokens when
# caching applies).

Invalid request or unsupported parameter

Check the model ID, the messages array, and parameter ranges against the API reference; remove fields this route does not support.

Authentication or balance issue

Check the Authorization bearer token and confirm the available balance in the console.

Context length exceeded

Prompt tokens exceed the Claude Fable 5.1 context window. Trim or retrieve only the relevant evidence and reuse cached prefixes.

Rate limited (429)

Back off and retry with jitter; batch or queue requests instead of sending parallel bursts.

Content or tool call rejected

Review sensitive content, malformed tool-call arguments, and JSON schema mismatches before retrying.

Adopt Claude Fable 5.1 without replacing your model stack

Keep one EvoLink client and API key, route the hardest workloads to Fable 5.1, and retain tested alternatives for simpler or latency-sensitive traffic.

01

Use the existing compatible client flow

Point the client at EvoLink, authenticate with the same API key, and select claude-fable-5-1. Both the OpenAI-compatible Chat Completions endpoint and the Anthropic Messages endpoint work.

Low migration
02

Use the documented API model ID

The API route is claude-fable-5-1 on both protocols. The page URL and the model parameter are identical for this model.

ID checked
03

Structure prompts for cache reuse

Put the stable system prompt, repository instructions, and tool schemas at the front of the request so the expensive prefix is written once and read cheaply for the rest of the session.

Cost control
04

Route tasks by completed-task value

Compare success rate, retries, output tokens, cache hits, wall-clock time, and human correction against Claude Opus 5 and Claude Fable 5 — not token price alone.

Evaluate

Prompt caching billed as two separate dimensions

Storing a prefix costs $11.875 per 1M tokens; reusing it costs $0.239 per 1M tokens. Stable system prompts, repository instructions, and tool schemas pay the write once and then use the separate cache-read rate across the run.

1M-token context with a 128K max output

Keep connected code, specifications, documents, and agent state in one working context. Treat the limit as capacity rather than a target: retrieve relevant evidence, cache the stable prefix, and set task-appropriate output budgets.

Thinking and effort change latency and token use

Anthropic enables adaptive thinking by default on Fable 5.1, and the Claude API defaults effort to high. Before production, verify parameter support on the EvoLink endpoint you use and measure the actual response, output tokens, and latency. Do not treat max_tokens as a thinking budget.

Replay real workloads before shifting production traffic

The same per-token rate does not guarantee the same completed-task cost. Model behavior and tokenizer changes can alter billed tokens, retries, and tool paths, so compare success rate, total cost, and human correction on production samples before shifting traffic.

Forced tool choice and thinking history require migration checks

Fable 5.1 rejects forced tool_choice values any and tool. Earlier Claude models also cannot read Fable 5.1 thinking blocks, and editing earlier turns invalidates those blocks, so keep conversation history append-only and test cross-model fallbacks before production routing.

Five billing dimensions, metered separately

Claude Fable 5.1 does not bill as a single blended rate. Understanding which dimension a workload actually consumes is what makes a top-tier budget predictable.

Input and output tokens

The two dimensions every request touches: $9.500 per 1M input tokens and $47.500 per 1M output tokens on EvoLink, compared with Anthropic’s $10.000 and $50.000. Output dominates on generation-heavy work, so cap max_tokens by task complexity.

Cache write and cache read

Storing a prefix costs $11.875 per 1M tokens; reusing it costs $0.239 per 1M tokens. Stable system prompts, repository instructions, and tool schemas pay the write once and then use the separate cache-read rate across the run.

Web search tool

Billed per search at $0.010. Search results also enter the request as ordinary input tokens, so a research-heavy turn pays both the per-search fee and the tokens it pulls in.

Compare Claude routes after workload testing

EvoLink

First verify whether Fable 5.1 reduces retries and review effort on your own tasks. Then compare price, context, caching, and workload fit to choose the production route.

Claude Fable 5.1
Input / output$9.5 / $47.5
Context1M
CachingRead + write
Best forRepository-scale software engineering, long-horizon agent runs with heavy tool use, high-stakes code review, and research or analysis work where a wrong answer costs more than a premium token rate.
Claude Fable 5
Input / output$9 / $45
Context1M
CachingRead + write
Best forThe previous Fable generation; compare its token and cache-read rates for your workload.
Claude Opus 5
Input / output$4.75 / $23.75
Context1M
CachingRead + write
Best forCompare Claude Opus 5’s current token rates and answer quality before choosing it as the default flagship route.

Claude Model Family

Same API key and balance — switch tiers without changing your integration.

Compare all Claude models
Claude Opus 5

Claude Opus 5

Compare Claude Opus 5’s current token rates and answer quality before choosing it as the default flagship route.

View model
Claude Sonnet 5

Claude Sonnet 5

A more balanced route for everyday coding, high-volume agents, and latency-sensitive production traffic.

View model
Claude Fable 5

Claude Fable 5

The previous Fable generation; compare its token and cache-read rates for your workload.

View model

Other text models on EvoLink besides Claude Fable 5.1

GPT-5.6

GPT-5.6

OpenAI’s tiered frontier family for routing across capability, latency, and cost.

View model
Grok 4.5

Grok 4.5

xAI’s reasoning and tool-use route with a 500K context window and server-side search tools.

View model
Kimi K3

Kimi K3

A long-context reasoning model for repository-scale coding and multi-document work.

View model
Gemini 3.6 Flash

Gemini 3.6 Flash

A fast, low-cost route for production traffic that does not need Opus-tier judgment.

View model

Related reading

Claude Fable 5.1 Release Date

Claude Fable 5.1 Release Date

Confirmed launch facts, channel boundaries, migration risks, and the production signals to verify after release.

Read guide
Claude Fable 5 vs Fable 5.1

Claude Fable 5 vs Fable 5.1

Compare cache economics, compatibility, successful-task cost, and a reversible upgrade path.

Read guide
Claude Fable 5.1 vs GPT-6 Astra

Claude Fable 5.1 vs GPT-6 Astra

Compare two released frontier models on cache economics, agent controls, and matched production evaluation.

Read guide
Claude Opus 5 vs Claude Fable 5

Claude Opus 5 vs Claude Fable 5

Decide when the Opus tier is the right default and whether Fable delivers enough value for a workload.

Read guide
Claude Fable 5 API Pricing

Claude Fable 5 API Pricing

Token costs, usage credits, and worked examples comparing Anthropic list pricing with EvoLink rates.

Read guide
Claude Opus 6 Release Watch

Claude Opus 6 Release Watch

Track the next Opus generation without treating its release date, API access, model ID, or pricing as confirmed.

Read guide

Claude Fable 5.1 API FAQ

Is the Claude Fable 5.1 API available through EvoLink?

Yes. Claude Fable 5.1 is available on EvoLink as a production route under model ID "claude-fable-5-1".

What model ID should I use for the Claude Fable 5.1 API?

Send model "claude-fable-5-1". The same ID works for both the OpenAI-compatible Chat Completions endpoint and the Anthropic Messages endpoint.

How much does the Claude Fable 5.1 API cost on EvoLink?

EvoLink pricing: $9.500 per 1M input tokens and $47.500 per 1M output tokens, against Anthropic’s $10.000 and $50.000.

How is Claude Fable 5.1 prompt caching billed?

Cache write and cache read are separate dimensions: $11.875 per 1M cache write tokens and about $0.239 per 1M cache read tokens on EvoLink, versus $12.500 and $0.250 official.

How is the Claude Fable 5.1 web search tool billed?

Web search is charged per search at $0.010. Tokens the search results add to the request are billed normally.

Which protocols and SDKs work with Claude Fable 5.1?

Use the OpenAI-compatible Chat Completions endpoint or the Anthropic Messages endpoint with the same EvoLink API key. Claude Code and other Anthropic-native clients work by pointing the base URL at EvoLink.

What context window and max output does Claude Fable 5.1 support?

The EvoLink route records a 1,000,000-token context window with up to 128K output tokens per response.

Is thinking enabled by default on Claude Fable 5.1?

Anthropic enables adaptive thinking by default on Fable 5.1, and the Claude API defaults effort to high. Confirm that the specific parameters you need pass through your selected EvoLink endpoint by checking the API docs and an actual response.

What workloads are a good fit for Claude Fable 5.1?

Claude Fable 5.1 fits especially demanding coding, long-running agents with heavy tool use, and critical reviews where errors create high downstream costs.

Does Claude Fable 5.1 support forced tool choice?

No. Requests using tool_choice any or tool return HTTP 400. Use auto or none and test tool routing before migration.

What changes when routing a Fable 5.1 conversation to another model?

Earlier Claude models cannot read Fable 5.1 thinking blocks. Preserve conversation history as append-only because editing earlier turns also invalidates those thinking blocks.