Claude Sonnet 5.5 vs Grok 4.5
Pricing, context window and real answers (September 2026)
Claude Sonnet 5.5 (Anthropic) and Grok 4.5 (xAI), 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 |  Grok 4.5 | |
|---|---|---|
| Provider | Anthropic | xAI |
| 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 | 500,000 tokens |
| Release date | 9/28/2026 | 7/8/2026 |
| Input modalities | text, image, file | text, image, file |
| Throughput (p50) | — | 117 tokens/s (n=17) |
| Arena · overall | Unranked | #47 · ELO 1,465 |
| Arena · Japanese | Unranked | #45 · ELO 1,438 |
| Arena · coding | Unranked | #47 · ELO 1,513 |
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, Grok 4.5: ¥1,072.2 per 1M output tokens, 40% less than Claude Sonnet 5.5.
- For long documents, Claude Sonnet 5.5: a 1,000,000-token context window against 500,000 for Grok 4.5.
- 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 5.5
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
Grok 4.5
The word "strawberry" is spelled as follows:
**s-t-r-a-w-b-e-r-r-y**
- Position 1: **s**
- Position 2: **t**
- Position 3: **r** ← (1st "r")
- Position 4: **a**
- Position 5: **w**
- Position 6: **b**
- Position 7: **e**
- Position 8: **r** ← (2nd "r")
- Position 9: **r** ← (3rd "r")
- Position 10: **y**
There are **3** occurrences of the letter "r".
6.5s350 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
Grok 4.5
The error occurs because `users` is `undefined` when the component renders, so calling `.map()` on it fails.
This commonly happens when:
- The parent component doesn’t pass a `users` prop at all
- The data is loaded asynchronously and is still `undefined` on the first render
- The prop is accidentally set to `undefined`/`null` instead of an array
### Fixes
**1. Default to an empty array (simplest)**
```js
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => (
<li key={user.id}>{user.name}</li>
))}
</ul>
);
}
```
**2. Optional chaining (also fine)**
```js
function UserList({ users }) {
return (
<ul>
{users?.map(user => (…
7.9s507 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
Grok 4.5
## Code Review: `get_data`
### Issues
| Area | Problem |
|------|---------|
| **Imports** | `requests` / `time` inside the function — re-imported on every call; belong at module level |
| **Exceptions** | Bare `except:` swallows `KeyboardInterrupt`, `SystemExit`, and hides bugs |
| **Boolean check** | `item["active"] == True` is unidiomatic; truthiness is enough |
| **Loop** | Manual `for` + `append` can be a list comprehension |
| **Retries** | Sleeps on non-200 but never logs or distinguishes failure modes; unused loop variable `i` |
| **Robustness** | No guard for non-list JSON, missing keys (`KeyError`), or invalid JSON |
| **API** | Magic numbers (`timeout=10`, `sleep=2`); no docstrin…
25.3s1363 output tokens
Frequently asked questions
- Which is cheaper, Claude Sonnet 5.5 or Grok 4.5?
- Per 1M output tokens, Claude Sonnet 5.5 is ¥1,787 and Grok 4.5 is ¥1,072.2 on FastMetal (yen, before tax), so Grok 4.5 is cheaper.
- How do the context windows of Claude Sonnet 5.5 and Grok 4.5 compare?
- Claude Sonnet 5.5 takes 1,000,000 tokens; Grok 4.5 takes 500,000.
- Can I use Claude Sonnet 5.5 and Grok 4.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-sonnet-5-5" or "grok-4.5" 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 Sonnet 5.5 and Grok 4.5 from the browser chat and the API. No monthly fee.