Claude Sonnet 5.5 vs Fugu Ultra v2
Pricing, context window and real answers (September 2026)
Claude Sonnet 5.5 (Anthropic) and Fugu Ultra v2 (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 5.5 | Fugu Ultra v2 | |
|---|---|---|
| Provider | Anthropic | Sakana AI |
| Input (per 1M tokens) | ¥357.4 | ¥893.5 |
| Output (per 1M tokens) | ¥1,787 | ¥5,361 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥1,251 | ¥3,574 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Release date | 9/28/2026 | 9/11/2026 |
| Input modalities | text, image, file | text, image, file |
| Throughput (p50) | — | — |
| Arena · overall | Unranked | Unranked |
| Arena · Japanese | Unranked | Unranked |
| Arena · coding | Unranked | Unranked |
Prices are FastMetal's yen rates before tax.
Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-09-25; category names mapped and ratings rounded by FastMetal.
Which should you pick?
- On price, Claude Sonnet 5.5: ¥1,787 per 1M output tokens, 67% less than Fugu Ultra v2.
- 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 5.5
Let me go through the word letter by letter.
**strawberry**
| Position | Letter |
|---|---|
| 1 | s |
| 2 | t |
| 3 | **r** ← 1st |
| 4 | a |
| 5 | w |
| 6 | b |
| 7 | e |
| 8 | **r** ← 2nd |
| 9 | **r** ← 3rd |
| 10 | y |
**Step-by-step reasoning:**
1. I split the word into individual letters: s-t-r-a-w-b-e-r-r-y (10 letters total).
2. I checked each letter for 'r'.
3. The first 'r' is in position 3, in "str…".
4. The second and third 'r's are in positions 8 and 9, in the "…rry" ending.
**Answer: There are 3 r's in "strawberry".**
A common mistake is to see "berry" as having only one 'r' (or to treat the double-r as a single letter), which leads to the incorrect answer of 2.
3.1s332 output tokens
Fugu Ultra v2
**Answer: 3**
**Step-by-step reasoning:**
1. **Write out the word letter by letter**, assigning each a position:
| Position | Letter | Is it 'r'? |
|---|---|---|
| 1 | s | no |
| 2 | t | no |
| 3 | **r** | ✅ yes |
| 4 | a | no |
| 5 | w | no |
| 6 | b | no |
| 7 | e | no |
| 8 | **r** | ✅ yes |
| 9 | **r** | ✅ yes |
| 10 | y | no |
2. **Tally the matches:** positions 3, 8, and 9 are 'r'.
3. **Sanity check by chunks:** "straw" contains one 'r' (str**a**w → the r in "str"), and "berry" contains two 'r's (be**rr**y). 1 + 2 = 3.
4. **Verify length:** the letters counted total 10, which matches the length of "strawberry" — so no letter was skipped or double-counted.
**Conclusion:** There a…
10.2s435 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 5.5
## Cause
`users` is `undefined` when the component renders, so `users.map(...)` throws. This happens when:
1. **The parent doesn't pass the prop**, or passes it under a different name (e.g. `<UserList data={x} />` or a typo like `user=`).
2. **The data loads asynchronously.** On the first render, the state or fetch result hasn't arrived yet.
3. **The value is wrong.** For example, the API returns `{ users: [...] }` and you passed the whole object, or you're reading a property that doesn't exist (`response.data.users` vs `response.users`).
## Fixes
### 1. Default value (simplest)
```jsx
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => <li key={user.id}>{use…
6.7s824 output tokens
Fugu Ultra v2
## What the error means
`TypeError: Cannot read properties of undefined (reading 'map')` means that when `UserList` rendered, `users` was `undefined`, and JavaScript can't read the `.map` property off `undefined`.
The important detail: **the bug isn't really in `UserList`** — that's just where it surfaces. Destructuring `function UserList({ users })` does *not* throw when the prop is missing; it silently gives you `undefined`. The crash is deferred to the first property access, which is `.map` on line 12.
So the real question is: why is `props.users` not an array?
## Why `users` is undefined
**1. Async data hasn't arrived yet — by far the most common cause.**
```jsx
const [users, setUs…
70.8s5286 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 5.5
# Code Review
## Main Issues
### 1. Bare `except:` hides bugs (most important)
It catches everything, including `KeyboardInterrupt` and `SystemExit`. It also wraps your parsing logic, so a missing `"active"` key (`KeyError`) or bad JSON is treated as a network failure, retried 3 times with sleeps, and then silently becomes `[]`. Catch only `requests.RequestException`, and keep parsing outside the `try`.
### 2. Silent failure
Returning `[]` after all retries fails is indistinguishable from "the server returned no active items." Callers can't tell whether something went wrong. Raise an exception (or at least log) once retries are exhausted.
### 3. Retry logic
- It sleeps after the final at…
20.9s3003 output tokens
Fugu Ultra v2
# Final Code Review: `get_data`
The function is compact and its intent is clear, but as written it will **fail silently in production**. Two defects dominate everything else:
1. The bare `except:` swallows every error — including `KeyboardInterrupt` and genuine logic bugs.
2. A total failure and a legitimately empty dataset both return `[]`, so callers cannot tell "the service is down" from "there are no active records."
Together these mean an outage looks exactly like a successful empty response. Everything else below is meaningful improvement; those two are the difference between code that fails loudly and code that fails invisibly.
---
## 1. Correctness and error handling
### 1.1 `e…
281.1s23317 output tokens
Frequently asked questions
- Which is cheaper, Claude Sonnet 5.5 or Fugu Ultra v2?
- Per 1M output tokens, Claude Sonnet 5.5 is ¥1,787 and Fugu Ultra v2 is ¥5,361 on FastMetal (yen, before tax), so Claude Sonnet 5.5 is cheaper.
- How do the context windows of Claude Sonnet 5.5 and Fugu Ultra v2 compare?
- Claude Sonnet 5.5 takes 1,000,000 tokens; Fugu Ultra v2 takes 1,000,000.
- Can I use Claude Sonnet 5.5 and Fugu Ultra v2 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-sonnet-5-5" or "fugu-ultra-v2" 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 5.5 and Fugu Ultra v2 from the browser chat and the API. No monthly fee.