What is the max output length for claude-fable-5-1?

claude-fable-5-1 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.

Can you call Claude Fable 5.1 with the SDK you already use?

Yes. Fable 5.1 is served through a compatible endpoint. You can continue using your existing SDK by changing the base URL and model ID.

How much does prompt caching save on claude-fable-5-1?

claude-fable-5-1 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-5-1.

When was Claude Fable 5.1 released, and is it still maintained?

Claude Fable 5.1 was released on 2026-09-01. Its catalog status is stable. Check the model page for deprecation notices before you build a long-lived integration on it.

Does Claude Fable 5.1 support tool calling and structured output?

Confirm the current capabilities in the model documentation. Fable 5.1 is designed for agentic workflows. Test with your specific tool definitions.

How should you set the output budget for claude-fable-5-1?

For claude-fable-5-1, 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.

How do you get a cache hit on claude-fable-5-1?

To get a cache hit on claude-fable-5-1, send requests with identical prompt prefixes. The cache is keyed by the beginning of your prompt; as long as the prefix matches a previous request, subsequent calls benefit from the lower cached rate. Keep system messages and initial context consistent across calls for best results.

Model detail

Claude Fable 5.1

Provided by Anthropic

Pay-as-you-go

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 code generation, and finance and analysis tasks in particular. It also tends to be more concise than Fable 5 in its plans and summaries. We recommend testing it as a direct upgrade wherever you use Fable 5 today, and alongside Opus 5 on reasoning-heavy tasks.

Model specs

Model ID: claude-fable-5-1

Context length: 1M
Max output: 128K
I/O modalities
Released: 2026-09

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

$0.2500 /1M Tokens

Cache creation

$12.5000 /1M Tokens

Selection summary

Quickly judge whether it fits your workload

What is this model good for?

Agentic coding, long-running workflows, and knowledge work

Use Claude Fable 5.1 for long code refactors, front-end and visual code generation, and finance and analysis tasks. It improves on Fable 5 with gains in agentic coding and knowledge work, and is more concise in plans and summaries.

What should you check before using it?

Test as a direct upgrade from Fable 5

Fable 5.1 is recommended as a direct upgrade wherever you use Fable 5. Also test alongside Opus 5 on reasoning-heavy tasks to find the best fit for your workload. Knowledge cutoff: 2026-06.

Why use it through MixRoute?

Claude Fable 5.1 cache reads cut repeated-prompt cost

Cached prefixes are billed at 0.25 USD per 1M tokens instead of 10 USD, so repeated system prompts cost less. MixRoute serves Claude Fable 5.1 on the OpenAI-compatible endpoint /v1/chat/completions; point your existing client at https://api.mixroute.ai/v1 with the model ID claude-fable-5-1 and re-run your integration tests.

Capabilities & compatibility

Unconfirmed capabilities stay "Unknown," no guesses

Tool calling

Claude Fable 5.1 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 5.1 can produce JSON-formatted output on demand.

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

Streaming

Claude Fable 5.1 supports streamed responses.

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

Prompt caching

Claude Fable 5.1 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 5.1 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 5.1 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 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work. It is particularly strong at long code refactors, front-end and visual code generation, and finance and analysis 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-5-1

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