How do you start calling Claude Fable 5?

Use the model ID claude-fable-5 through the compatible chat completions endpoint. It supports text, image, and file inputs with text output.

Does claude-fable-5 have a free tier?

Claude Fable 5 is billed per use and the record publishes no free-tier allowance. The current published rates are input $10.0000 per 1M tokens and output $50.0000 per 1M tokens. Trial credit or promotional quota is tied to your account rather than to the model, so check the console before planning around a free tier.

What should you evaluate before moving production traffic to Claude Fable 5?

Test your long-running autonomous tasks and verify the self-correction and verification loop behavior. Fable 5 is designed for tasks that would otherwise take hours or days.

What is the max output length for claude-fable-5?

claude-fable-5 supports up to 128000 output tokens per request. Plan your prompts to stay within this limit, and use the max_tokens or max_completion_tokens parameter to control output length.

Does Claude Fable 5 support tool calling and structured output?

Confirm the current capabilities in the model documentation. Fable 5 is built for autonomous knowledge work and ships with robust safeguards.

How much does prompt caching save on claude-fable-5?

claude-fable-5 supports prompt caching, which can significantly reduce costs for repeated prompts with shared prefixes. The cache read price is substantially lower than the standard input price. Check the current pricing page for the exact cache hit discount ratio for claude-fable-5.

How should you set the output budget for claude-fable-5?

For claude-fable-5, set the max_tokens or max_completion_tokens parameter to control spending per call. Start with a budget aligned to your typical response length and increase only when longer outputs are genuinely needed. Monitor token usage in the API response headers to tune your budget over time.

Model detail

Claude Fable 5

Provided by Anthropic

Pay-as-you-go

Claude Fable 5 is a Mythos-class model from Anthropic, built for autonomous knowledge work and coding. It supports text, image, and file inputs with text output, with reasoning support and a 1M-token context window. It is suited for long-running, complex, and asynchronous tasks that previously required frequent human check-ins. It is particularly strong at end-to-end work that would otherwise take a person hours, days, or weeks - taking on problems that are long-running, ambiguous, or highly multi-step. It executes well-scoped tasks with few mistakes, automatically self-correcting through verification loops, and ships with robust safeguards.

Model specs

Model ID: claude-fable-5

Context length: 1M
Max output: 128K
I/O modalities
Released: 2026-06

API endpoints

One MixRoute gateway, OpenAI-compatible

Anthropic Messages /v1/messages POST
OpenAI-compatible /v1/chat/completions POST

Pricing

Flat rate, unit: /1M Tokens

Input

$10.0000 /1M Tokens

Completion

$50.0000 /1M Tokens

Cache read

$1.0000 /1M Tokens

Cache creation

$12.5000 /1M Tokens

Selection summary

Quickly judge whether it fits your workload

What is this model good for?

Autonomous knowledge work and coding with 1M context

Use Claude Fable 5 for long-running, complex, and asynchronous tasks. It supports text, image, and file inputs with a 1M-token context window, and self-corrects through verification loops.

What should you check before using it?

Test autonomous task execution and verification

Fable 5 is built for tasks that previously required frequent human check-ins. Test your multi-step workflows and verify the self-correction behavior meets your quality requirements. Knowledge cutoff: 2026-01.

Why use it through MixRoute?

Claude Fable 5 keeps its 1,000,000-token context on one route

The full 1,000,000-token context stays reachable on the same route. MixRoute serves Claude Fable 5 on the OpenAI-compatible endpoint /v1/chat/completions; point your existing client at https://api.mixroute.ai/v1 with the model ID claude-fable-5 and re-run your integration tests.

Capabilities & compatibility

Unconfirmed capabilities stay "Unknown," no guesses

Tool calling

Claude Fable 5 supports function and tool calls.

EX Send a tools definition; the response returns tool_calls to execute and feed results back.

Structured output

Claude Fable 5 can produce JSON-formatted output on demand.

EX response_format: { type: "json_schema" } forces valid JSON output.

Streaming

Claude Fable 5 supports streamed responses.

EX stream: true streams tokens incrementally, so chat UIs render as they arrive.

Prompt caching

Claude Fable 5 supports prompt caching under supported routing conditions.

EX Keep the system prompt and tool definitions at the start of the request; repeated prefixes are automatically billed at the cache-read rate.

Vision input

Claude Fable 5 can process image inputs alongside text.

EX Pass a base64-encoded image in a image_url content part alongside text messages.

OpenAI SDK

Call Claude Fable 5 through MixRoute's OpenAI-compatible endpoint.

EX Change base_url to https://api.mixroute.ai/v1; everything else follows the OpenAI style.

Token cost estimator

Live estimate from this page's pricing, not an actual bill

Input tokens Max per request 1M

Output tokens Max per request 128K

Requests / month

Cache hit rate 0%

Share of the same prefix read repeatedly, up to 100%

FAQ

Claude Fable 5 is a Mythos-class model from Anthropic, built for autonomous knowledge work and coding. It supports text, image, and file inputs with a 1M-token context window and is suited for long-running, complex, asynchronous tasks.

Get started

01

Create an API key

Generate a key in the Console; one key calls every model.
02

Set the base URL

Fully OpenAI SDK-compatible; just swap the URL to connect.

https://api.mixroute.ai/v1
03

Specify the model ID

In the request's model field, enter:

claude-fable-5

Create an API key

New users get $5 in free credits

Test this model and alternate routes with the same request format

Start from a real workload, then let quality, total cost, and failure conditions decide whether to send production traffic.

Create an API key View integration docs