Claude Fable 5.1 vs Claude Haiku 5.5
Pricing, context window and real answers (October 2026)
Claude Fable 5.1 (Anthropic) and Claude Haiku 5.5 (Anthropic), 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 | Claude Haiku 5.5 | |
|---|---|---|
| Provider | Anthropic | Anthropic |
| Input (per 1M tokens) | $10.55 | $0.1055 |
| Output (per 1M tokens) | $52.75 | $0.5275 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | $36.93 | $0.3693 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Release date | 9/1/2026 | 10/7/2026 |
| Input modalities | text, image, file | text, image, file |
| Throughput (p50) | 271 tokens/s (n=25) | — |
| Arena · overall | #6 · ELO 1,501 | Unranked |
| Arena · Japanese | #1 · ELO 1,542 | Unranked |
| Arena · coding | #19 · ELO 1,531 | Unranked |
Prices are FastMetal's rates, before tax.
Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-10-02; category names mapped and ratings rounded by FastMetal.
Which should you pick?
- On price, Claude Haiku 5.5: $0.5275 per 1M output tokens, 99% less than 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
Claude Haiku 5.5
There are **3** r's in "strawberry."
1. **Spell out the word:** s, t, r, a, w, b, e, r, r, y
2. **Go through each letter and count the r's:**
- Position 3: **r** (count = 1)
- Position 8: **r** (count = 2)
- Position 9: **r** (count = 3)
3. **Check the rest:** s, t, a, w, b, e, and y are not r's.
Total: **3**
2.4s200 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
Claude Haiku 5.5
The error means `users` is `undefined` when `UserList` renders, so `.map` is called on nothing. The component destructures the `users` prop, but the parent didn't pass it, or passed `undefined`.
## Common causes
**1. The parent doesn't pass the prop, or uses a different name**
```jsx
<UserList /> // users is undefined
<UserList user={users} /> // wrong name: "user" instead of "users"
```
**2. The data hasn't loaded yet (most common with fetched data)**
```jsx
function App() {
const [users, setUsers] = useState(); // undefined initially
useEffect(() => {
fetch('/api/users').then(r => r.json()).then(setUsers);
}, []);
return <UserList users={users} />;…
5.1s888 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
Claude Haiku 5.5
## Issues
**Correctness and robustness**
1. **Bare `except:`** catches everything, including `KeyboardInterrupt` and `SystemExit`, so Ctrl+C may not stop the program. Catch specific exceptions: `requests.RequestException` for network problems and `ValueError` for invalid JSON.
2. **Retries non-retryable errors.** A 404 or 401 won't succeed on retry, so retrying wastes time. Only retry transient failures such as 429, 5xx, timeouts, and connection errors.
3. **Sleeps after the final attempt.** The loop sleeps even when no retry follows.
4. **Fixed sleep with no backoff.** Exponential backoff is the standard approach for retries.
5. **Silent failure.** Every failure returns `[]` with no loggin…
18.1s4096 output tokens
Frequently asked questions
- Which is cheaper, Claude Fable 5.1 or Claude Haiku 5.5?
- Per 1M output tokens, Claude Fable 5.1 is $52.75 and Claude Haiku 5.5 is $0.5275 on FastMetal (US dollars, before tax), so Claude Haiku 5.5 is cheaper.
- How do the context windows of Claude Fable 5.1 and Claude Haiku 5.5 compare?
- Claude Fable 5.1 takes 1,000,000 tokens; Claude Haiku 5.5 takes 1,000,000.
- Can I use Claude Fable 5.1 and Claude Haiku 5.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-fable-5-1" or "anthropic-claude-haiku-5-5" 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 Claude Haiku 5.5 from the browser chat and the API. No monthly fee.