Claude Opus 4.8 vs Grok 4.5
Pricing, context window and real answers (August 2026)
Claude Opus 4.8 (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 4.8 |  Grok 4.5 | |
|---|---|---|
| Provider | Anthropic | xAI |
| Input (per 1M tokens) | ¥893.5 | ¥357.4 |
| Output (per 1M tokens) | ¥4,467.5 | ¥1,072.2 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥3,127 | ¥894 |
| Context window | 1,000,000 tokens | 500,000 tokens |
| Release date | 5/27/2026 | 7/8/2026 |
| Input modalities | text, image, file | text, image, file |
| Arena · overall | #22 · ELO 1,474 | #35 · ELO 1,468 |
| Arena · Japanese | #26 · ELO 1,448 | Unranked |
| Arena · coding | #12 · ELO 1,528 | #28 · ELO 1,516 |
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, 76% less than Claude Opus 4.8.
- On the Overall arena board, Claude Opus 4.8 ranks higher (#22; Grok 4.5 is #35).
- On the Coding arena board, Claude Opus 4.8 ranks higher (#12; Grok 4.5 is #28).
- For long documents, Claude Opus 4.8: 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 4.8
# Counting 'r's in "strawberry"
## Step-by-step process:
Let me go through each letter one at a time:
| Position | Letter | Is it 'r'? |
|----------|--------|-----------|
| 1 | s | No |
| 2 | t | No |
| 3 | r | ✓ Yes (1) |
| 4 | a | No |
| 5 | w | No |
| 6 | b | No |
| 7 | e | No |
| 8 | r | ✓ Yes (2) |
| 9 | r | ✓ Yes (3) |
| 10 | y | No |
## Answer:
There are **3** 'r's in "strawberry".
The three 'r's appear at positions 3, 8, and 9 — one after the "st" and two together in the "rry" ending.
4.5s262 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 4.8
# What's Causing the Error
The error tells you exactly what's happening:
```
TypeError: Cannot read properties of undefined (reading 'map')
at UserList (/app/components/UserList.js:12:25)
```
At the moment `UserList` renders, the `users` prop is `undefined`, and you can't call `.map()` on `undefined`. This is extremely common when data is fetched asynchronously—the component renders **before** the data arrives.
Common reasons `users` is undefined:
- The parent hasn't passed the `users` prop at all
- Data is still loading from an API (initial state is `undefined`)
- The API response shape differs from what you expect (e.g. `data.users` vs `data`)
---
# How to Fix It
## Option 1: De…
11.3s761 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 4.8
# Code Review
Here's a breakdown of issues and suggested improvements for your function.
## Key Issues
1. **Imports inside the function** — should be at module level (runs on every call, harder to see dependencies).
2. **Bare `except:`** — catches everything, including `KeyboardInterrupt` and `SystemExit`. Silently swallowing errors makes debugging hard.
3. **Magic numbers** — `10`, `2`, `200` scattered around; extract as parameters/constants.
4. **`== True` comparison** — non-Pythonic; use the value directly (or `is True` if strict).
5. **Blocking `time.sleep(2)`** — fixed delay; exponential backoff is a better practice.
6. **`r.status_code == 200`** — misses other success codes; use `ra…
16.9s1403 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 4.8 or Grok 4.5?
- Per 1M output tokens, Claude Opus 4.8 is ¥4,467.5 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 4.8 and Grok 4.5 compare?
- Claude Opus 4.8 takes 1,000,000 tokens; Grok 4.5 takes 500,000.
- Which ranks higher, Claude Opus 4.8 or Grok 4.5?
- Claude Opus 4.8 ranks higher on the public arena (Claude Opus 4.8 #26, Grok 4.5 #35). Ranks move as the leaderboard updates.
- Can I use Claude Opus 4.8 and Grok 4.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-opus-4-8" 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 4.8 and Grok 4.5 from the browser chat and the API. No monthly fee.