How much does the Claude Fable 5.1 API cost?

On FastMetal, Claude Fable 5.1 is billed per token in yen: ¥1,787 per 1M input tokens and ¥8,935 per 1M output tokens, before tax. Usage is drawn from a prepaid balance; there is no subscription or monthly fee.

Can I call Claude Fable 5.1 with the OpenAI SDK?

Yes. Point base_url at https://api.fastmetal.ai/v1 and pass "anthropic-claude-fable-5-1" as the model; existing OpenAI-style code works unchanged, including streaming, tool calls and structured output.

What is the context window of Claude Fable 5.1?

1,000,000 tokens, shared between the prompt and the response.

What do I need to try Claude Fable 5.1?

Create an account and add credit; the model is then available both in the browser chat and over the API. There is no contract or minimum spend.

Back to Models

anthropic/claude-fable-5-1

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...

9/1/2026

1,000,000 tokens

Input: ¥1,787/M

Output: ¥8,935/M

Try in Chat Get API Key

Specifications

Modalities

Input

text

image

file

Output

text

Supported Parameters

include_reasoning

max_completion_tokens

max_tokens

reasoning

reasoning_effort

response_format

stop

structured_outputs

tools

verbosity

Max Output Tokens

128,000

Reasoning Configuration

Default: Thinking on (effort: high)
Selectable effort levels: max
xhigh
high
medium
low
Turning thinking off: Not possible (always thinks)

How to control thinking, and what it costs

Code Examples

curl https://api.fastmetal.ai/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "anthropic-claude-fable-5-1",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

How Claude Fable 5.1 actually answers

Real responses to our standard prompts, recorded on FastMetal.

Count the number of 'r's in 'strawberry'

Count the number of 'r's in 'strawberry'. Explain your reasoning step by step.

**Step 1: Write out the word letter by letter.** s - t - r - a - w - b - e - r - r - y **Step 2: Number each position.** 1. s 2. t 3. **r** 4. a 5. w 6. b 7. e 8. **r** 9. **r** 10. y **Step 3: Identify which positions contain 'r'.** - Position 3: r (in "str-") - Position 8: r (in "-ber-") - Position 9: r (in "-rry") **Step 4: Count them.** 3 + 1 + 1 = **3** **Answer: There are 3 'r's in "strawberry."** A helpful way to check: split the word into its parts — "straw" (1 r) + "berry" (2 r's) = 3 r's total.

7.9s response259 output tokens

Debug This Error

I'm getting the following error in my Node.js application: TypeError: Cannot read properties of undefined (reading 'map') at UserList (/app/components/UserList.js:12:25) at renderWithHooks (/app/node_modules/rea…

The error means that when `UserList` rendered, the `users` prop was `undefined`, so calling `.map()` on it failed. This typically happens because: 1. **The parent isn't passing the prop** (or misspelled it, e.g. `<UserList user={...} />`), or 2. **The data hasn't loaded yet.** A common pattern is fetching users in a `useEffect` and storing them in state whose initial value is `undefined` (e.g. `useState()`), so the first render happens before the data arrives. **Fixes** Give the prop a default value so the component is safe to render with no data: ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => <li key={user.id}>{user.name}</li>)} </ul> ); }…

10.8s response564 output tokens

Code Review

Please review the following Python function and suggest improvements for readability, performance, and best practices: def get_data(url, retries=3): import requests import time for i in range(retries):…

Here's a review of the function organized by category, followed by a refactored version. ## Issues ### Correctness / robustness 1. **Bare `except:`** — This catches *everything*, including `KeyboardInterrupt`, `SystemExit`, and bugs like `KeyError` from `item["active"]`. A malformed response would be silently retried three times and then swallowed. Catch `requests.RequestException` (and `ValueError` for bad JSON) specifically. 2. **Retrying non-retryable errors** — A 404 or 400 will never succeed on retry. Only retry on transient failures (timeouts, connection errors, 5xx, 429). 3. **Silent failure** — Returning `[]` after exhausting retries is indistinguishable from "the endpoint legitima…

27.7s response2028 output tokens

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Frequently asked questions

How much does the Claude Fable 5.1 API cost?: On FastMetal, Claude Fable 5.1 is billed per token in yen: ¥1,787 per 1M input tokens and ¥8,935 per 1M output tokens, before tax. Usage is drawn from a prepaid balance; there is no subscription or monthly fee.
Can I call Claude Fable 5.1 with the OpenAI SDK?: Yes. Point base_url at https://api.fastmetal.ai/v1 and pass "anthropic-claude-fable-5-1" as the model; existing OpenAI-style code works unchanged, including streaming, tool calls and structured output.
What is the context window of Claude Fable 5.1?: 1,000,000 tokens, shared between the prompt and the response.
What do I need to try Claude Fable 5.1?: Create an account and add credit; the model is then available both in the browser chat and over the API. There is no contract or minimum spend.