Claude Fable 5.1 vs GPT-4.1 Nano
Pricing, context window and real answers (September 2026)
Claude Fable 5.1 (Anthropic) and GPT-4.1 Nano (OpenAI), compared as you can actually call them on FastMetal. Both are served from the same OpenAI-compatible endpoint and API key; switching is a change to the model string.
Specs and pricing
 Claude Fable 5.1 |  GPT-4.1 Nano | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input (per 1M tokens) | ¥1,787 | ¥17.87 |
| Output (per 1M tokens) | ¥8,935 | ¥71.48 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥6,255 | ¥54 |
| Context window | 1,000,000 tokens | 1,047,576 tokens |
| Release date | 9/1/2026 | 4/14/2025 |
| Input modalities | text, image, file | image, text, file |
| Throughput (p50) | — | — |
| Arena · overall | #5 · ELO 1,498 | #243 · ELO 1,322 |
| Arena · Japanese | Unranked | #195 · ELO 1,234 |
| Arena · coding | #32 · ELO 1,519 | #226 · ELO 1,374 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, GPT-4.1 Nano: ¥71.48 per 1M output tokens, 99% less than Claude Fable 5.1.
- On the Overall arena board, Claude Fable 5.1 ranks higher (#5; GPT-4.1 Nano is #243).
- On the Coding arena board, Claude Fable 5.1 ranks higher (#32; GPT-4.1 Nano is #226).
- For long documents, GPT-4.1 Nano: a 1,047,576-token context window against 1,000,000 for Claude Fable 5.1.
- If in doubt, try both on the same key. Switching is a change to the model string, and each is billed at its own rate.
Real answers to the same prompts
Exactly what the FastMetal gateway returned, side by side. Not benchmark scores: actual output.
Count the number of 'r's in 'strawberry'
Count the number of 'r's in 'strawberry'. Explain your reasoning step by step.
Claude Fable 5.1
**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.
7.9s259 output tokens
GPT-4.1 Nano
Let's analyze the word "strawberry" step by step to count the number of 'r's.
1. Write down the word: **strawberry**
2. Examine each letter one by one:
- s: no
- t: no
- r: yes (first 'r')
- a: no
- w: no
- b: no
- e: no
- r: yes (second 'r')
- r: yes (third 'r')
- y: no
3. Counting the 'r's found:
- First 'r' (at position 3)
- Second 'r' (at position 8)
- Third 'r' (at position 9)
So, there are **3** 'r's in "strawberry."
**Final answer: 3**
2.0s183 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…
Claude Fable 5.1
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>
);
}…
10.8s564 output tokens
GPT-4.1 Nano
The error:
```
TypeError: Cannot read properties of undefined (reading 'map')
```
indicates that `users` is `undefined` at the time your `UserList` component is rendering, and you're trying to call `map` on it.
### Why is this happening?
In React, if a prop (`users` in this case) is not provided or is undefined, trying to do `users.map(...)` causes this error. This can happen if:
- The parent component does not pass `users`.
- `users` might be `null` or `undefined` initially, especially if data fetching is involved.
### How to fix it
**Option 1: Provide a default value for `users`**
Ensure that `users` defaults to an empty array if it is not provided:
```jsx
function UserList({ users…
4.3s514 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):…
Claude Fable 5.1
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…
27.7s2028 output tokens
GPT-4.1 Nano
Here's a review and an improved version of your function:
### Key improvements:
1. **Move imports to the top**: Imports should generally be at the top of the file, not inside functions.
2. **Specify exception types**: Catch specific exceptions rather than a generic `except`.
3. **Use context managers if needed**: Not necessary here, but good to consider.
4. **Avoid repeated code**: The sleep statement is the same whether there is a request exception or a non-200 status.
5. **Simplify filtering**: Use list comprehensions for clarity.
6. **Improve variable names**: For readability.
7. **Add optional headers or parameters** if needed (not required here).
8. **Optional:** Add more descriptive e…
3.4s391 output tokens
Frequently asked questions
- Which is cheaper, Claude Fable 5.1 or GPT-4.1 Nano?
- Per 1M output tokens, Claude Fable 5.1 is ¥8,935 and GPT-4.1 Nano is ¥71.48 on FastMetal (yen, before tax), so GPT-4.1 Nano is cheaper.
- How do the context windows of Claude Fable 5.1 and GPT-4.1 Nano compare?
- Claude Fable 5.1 takes 1,000,000 tokens; GPT-4.1 Nano takes 1,047,576.
- Which ranks higher, Claude Fable 5.1 or GPT-4.1 Nano?
- Claude Fable 5.1 ranks higher on the public arena (Claude Fable 5.1 #5, GPT-4.1 Nano #195). Ranks move as the leaderboard updates.
- Can I use Claude Fable 5.1 and GPT-4.1 Nano with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-fable-5-1" or "gpt-4.1-nano" as the model. Each is billed at its own rate from the same prepaid balance.
Try both on one API key
Create an account and add credit to call Claude Fable 5.1 and GPT-4.1 Nano from the browser chat and the API. No monthly fee.