Claude Opus 5.5 vs Grok 4.5
Pricing, context window and real answers (September 2026)
Claude Opus 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 Opus 5.5 |  Grok 4.5 | |
|---|---|---|
| Provider | Anthropic | xAI |
| Input (per 1M tokens) | ¥692.4 | ¥357.4 |
| Output (per 1M tokens) | ¥3,462 | ¥1,072.2 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥2,423 | ¥894 |
| Context window | 1,000,000 tokens | 500,000 tokens |
| Release date | 9/22/2026 | 7/8/2026 |
| Input modalities | text, image, file | text, image, file |
| Throughput (p50) | — | — |
| Arena · overall | Unranked | #42 · ELO 1,468 |
| Arena · Japanese | Unranked | #37 · ELO 1,443 |
| Arena · coding | Unranked | #33 · ELO 1,518 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Grok 4.5: ¥1,072.2 per 1M output tokens, 69% less than Claude Opus 5.5.
- For long documents, Claude Opus 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 Opus 5.5
# Counting 'r's in "strawberry"
**Step 1: Spell out the word letter by letter.**
| Position | Letter |
|----------|--------|
| 1 | s |
| 2 | t |
| 3 | **r** ← |
| 4 | a |
| 5 | w |
| 6 | b |
| 7 | e |
| 8 | **r** ← |
| 9 | **r** ← |
| 10 | y |
**Step 2: Mark each 'r'.**
- Position 3: the "r" in "st**r**aw"
- Positions 8 and 9: the double "rr" in "be**rr**y"
**Step 3: Add them up.**
1 (in "straw") + 2 (in "berry") = **3**
**Answer: There are 3 'r's in "strawberry."**
A common mistake is to count only 2, because the double "rr" in "berry" can be read as a single sound. Breaking the word into its parts, "straw" + "berry," makes all three easy to see.
5.4s376 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 Opus 5.5
## What's causing it
The error means `users` is `undefined` when `UserList` renders, so `users.map(...)` fails. The component itself is fine. The problem is the value it receives from its parent. Common reasons:
1. **Async data hasn't loaded yet.** This is the most common cause. The parent fetches users from an API, and on the first render the state is still `undefined`:
```jsx
const [users, setUsers] = useState(); // undefined on first render
useEffect(() => {
fetch('/api/users').then(r => r.json()).then(setUsers);
}, []);
return <UserList users={users} />; // crashes before fetch completes
```
2. **The prop isn't being passed**, or has a different name:
```js…
10.9s1040 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 Opus 5.5
# Code Review: `get_data`
The function works in the happy path, but it has several issues that can hide bugs, waste time, and make failures hard to diagnose.
## Issues
### 🔴 Correctness and Reliability
**1. The bare `except:` is the most serious problem.**
It catches everything, including `KeyboardInterrupt`, `SystemExit`, and bugs in your own code. For example, if an item is missing the `"name"` key, the resulting `KeyError` gets swallowed and the request is retried as if it were a network error. The same happens with invalid JSON. Catch only the exceptions you expect, such as `requests.ConnectionError` and `requests.Timeout`.
**2. Failure is indistinguishable from "no results."**
Ret…
33.5s4023 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 Opus 5.5 or Grok 4.5?
- Per 1M output tokens, Claude Opus 5.5 is ¥3,462 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 Opus 5.5 and Grok 4.5 compare?
- Claude Opus 5.5 takes 1,000,000 tokens; Grok 4.5 takes 500,000.
- Can I use Claude Opus 5.5 and Grok 4.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-opus-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 Opus 5.5 and Grok 4.5 from the browser chat and the API. No monthly fee.