Claude Sonnet 5 vs Fugu Max
Pricing, context window and real answers (September 2026)
Claude Sonnet 5 (Anthropic) and Fugu Max (Sakana AI), 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 Sonnet 5 | Fugu Max | |
|---|---|---|
| Provider | Anthropic | Sakana AI |
| Input (per 1M tokens) | ¥357.4 | ¥357.4 |
| Output (per 1M tokens) | ¥1,787 | ¥1,072.2 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥1,251 | ¥894 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Release date | 6/30/2026 | 9/11/2026 |
| Input modalities | text, image, file | text, image, file |
| Throughput (p50) | — | — |
| Arena · overall | #51 · ELO 1,461 | Unranked |
| Arena · Japanese | #30 · ELO 1,448 | Unranked |
| Arena · coding | #27 · ELO 1,520 | Unranked |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Fugu Max: ¥1,072.2 per 1M output tokens, 40% less than Claude Sonnet 5.
- 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 Sonnet 5
# Counting 'r's in "strawberry"
**Step 1: Spell out the word letter by letter**
s - t - r - a - w - b - e - r - r - y
**Step 2: Number each letter position**
| Position | Letter |
|----------|--------|
| 1 | s |
| 2 | t |
| 3 | **r** |
| 4 | a |
| 5 | w |
| 6 | b |
| 7 | e |
| 8 | **r** |
| 9 | **r** |
| 10 | y |
**Step 3: Identify and count the 'r's**
- Position 3: **r** ✓ (1st r)
- Position 8: **r** ✓ (2nd r)
- Position 9: **r** ✓ (3rd r)
**Answer: There are 3 r's in "strawberry"**
5.9s405 output tokens
Fugu Max
The word **“strawberry”** has **3** letters **“r”**.
Step by step:
1. Write the word: **s t r a w b e r r y**
2. Check each letter:
- s — no
- t — no
- **r** — yes, 1st
- a — no
- w — no
- b — no
- e — no
- **r** — yes, 2nd
- **r** — yes, 3rd
- y — no
So, the total number of **‘r’s** in **“strawberry”** is **3**.
3.7s261 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 Sonnet 5
# Root Cause
The `UserList` component receives `users` as a prop, but at the time it's rendered, `users` is `undefined` — not an empty array, but literally missing. When your code tries to call `.map()` on `undefined`, JavaScript throws that `TypeError`.
This typically happens when:
- The parent component hasn't fetched the data yet (e.g., an API call is still in progress)
- The prop name doesn't match what's being passed down (typo)
- The data source (API/state) genuinely returns `undefined` in some case
# Fixes
**1. Add a default prop value (quick fix)**
```jsx
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => <li key={user.id}>{user.name}</li>)}
</u…
8.8s750 output tokens
Fugu Max
The error means `users` is `undefined` when `UserList` renders, so `users.map(...)` throws:
```js
function UserList({ users }) {
// if `users` is not passed, this is undefined
return (
<ul>
{users.map(user => <li key={user.id}>{user.name}</li>)}
</ul>
);
}
```
Common causes:
1. Parent renders `<UserList />` without the `users` prop.
2. State is initialized as `undefined`:
```js
const [users, setUsers] = useState();
```
3. Async data hasn’t loaded yet, but the component already renders.
4. The API returned something unexpected, e.g. `undefined`, an object, or an error response.
## Fixes
### 1. Default the prop to an empty array
```jsx
function UserList({ use…
10.6s1293 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 Sonnet 5
## Review of `get_data` Function
Here's an improved version followed by an explanation of the changes:
```python
import logging
import time
from typing import Any
import requests
logger = logging.getLogger(__name__)
def get_data(
url: str,
retries: int = 3,
timeout: float = 10.0,
backoff_factor: float = 2.0,
) -> list[dict[str, Any]]:
"""
Fetch active items from the given URL.
Args:
url: The endpoint to fetch data from.
retries: Number of attempts before giving up.
timeout: Request timeout in seconds.
backoff_factor: Multiplier for exponential backoff between retries.
Returns:
A list of dicts with "name" and "id"…
14.0s1299 output tokens
Fugu Max
Here’s a review with concrete improvements.
## Main issues
1. **Bare `except:`**
- Catches everything, including `KeyboardInterrupt`, `SystemExit`, and programming errors.
- Catch `requests.RequestException` instead, plus `ValueError` for JSON parsing if needed.
2. **Retries everything, including non-retryable errors**
- A `404` or `401` will be retried even though retrying will not help.
- Retry only transient failures: network errors, `429`, and `5xx`.
3. **Fixed 2-second sleep**
- No exponential backoff. Repeated retries can hammer the server.
- Use exponential backoff, optionally with jitter.
4. **Silent failure**
- Returning `[]` after all retries makes it hard…
24.7s3795 output tokens
Frequently asked questions
- Which is cheaper, Claude Sonnet 5 or Fugu Max?
- Per 1M output tokens, Claude Sonnet 5 is ¥1,787 and Fugu Max is ¥1,072.2 on FastMetal (yen, before tax), so Fugu Max is cheaper.
- How do the context windows of Claude Sonnet 5 and Fugu Max compare?
- Claude Sonnet 5 takes 1,000,000 tokens; Fugu Max takes 1,000,000.
- Can I use Claude Sonnet 5 and Fugu Max with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-sonnet-5" or "fugu-max" 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 Sonnet 5 and Fugu Max from the browser chat and the API. No monthly fee.