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anthropic/claude-fable-5

Claude Fable 5

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...

6/9/2026
1,000,000 tokens
#1 Text (Overall)
Input: ¥1,787/M
Output: ¥8,935/M
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
tool_choice
tools
verbosity

Max Output Tokens

128,000
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",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

How Claude Fable 5 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.

# Counting 'r's in "strawberry" Let me spell out the word letter by letter and check each one: | Position | Letter | Is it 'r'? | |----------|--------|------------| | 1 | s | No | | 2 | t | No | | 3 | **r** | ✅ Yes (1st) | | 4 | a | No | | 5 | w | No | | 6 | b | No | | 7 | e | No | | 8 | **r** | ✅ Yes (2nd) | | 9 | **r** | ✅ Yes (3rd) | | 10 | y | No | ## Reasoning breakdown: - The word "strawberry" can be split into two parts: **straw** + **berry** - "straw" contains one 'r': st**r**aw - "berry" contains two 'r's: be**rr**y (a double-r) ## Answer: **3** There are **three 'r's** in "strawberry."
39.6s response354 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…

## Cause The error means that when `UserList` renders, the `users` prop is `undefined`, so calling `.map()` on it fails. This typically happens for one of these reasons: 1. **The parent isn't passing the prop** (or has a typo in the prop name): ```jsx <UserList /> // users is undefined <UserList user={users} /> // typo: "user" instead of "users" ``` 2. **Data is fetched asynchronously** — the component renders before the API call finishes, and the initial state is `undefined`: ```jsx const [users, setUsers] = useState(); // undefined initially! ``` ## Fixes **Option 1: Default parameter value** (quick fix) ```jsx function UserList({ users = [] }) { re…
51.3s response686 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):…

# Code Review Your function works, but there are several issues worth addressing. Here's a breakdown by category: ## Issues Found ### 1. **Bare `except:` clause (critical)** This catches *everything*, including `KeyboardInterrupt`, `SystemExit`, and bugs like `KeyError` or `TypeError` in your own parsing code. You'll silently retry on programming errors and mask real problems. ### 2. **Imports inside the function** Imports belong at module level (PEP 8). Function-level imports add overhead on each call and hide dependencies. ### 3. **`== True` comparison** Use truthiness directly: `if item["active"]:` (PEP 8 explicitly recommends this). ### 4. **Silent failures** Returning `[]` on fail…
38.5s response1528 output tokens

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Try Claude Fable 5 right now

Claude Fable 5 is available on FastMetal through one API key. Start in the browser, or call it from the OpenAI SDK.

Leaderboard
Text
🏆OverallELO: 1,508
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🇯🇵JapaneseELO: 1,529
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🇨🇳ChineseELO: 1,558
#2
🇰🇷KoreanELO: 1,500
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🇬🇧EnglishELO: 1,514
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frenchELO: 1,538
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germanELO: 1,501
#5
spanishELO: 1,511
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russianELO: 1,515
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💻CodingELO: 1,552
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🧮MathELO: 1,539
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✍️Creative WritingELO: 1,507
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📝Instruction FollowingELO: 1,515
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🌶️Hard PromptsELO: 1,535
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💬Multi-TurnELO: 1,517
#4
Vision
🏆OverallELO: 1,318
#1
Code
🏆OverallELO: 1,630
#4