Grok 4.6 vs Mercury 2.5
Pricing, context window and real answers (September 2026)
Grok 4.6 (xAI) and Mercury 2.5 (Inception), 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
 Grok 4.6 | Mercury 2.5 | |
|---|---|---|
| Provider | xAI | Inception |
| Input (per 1M tokens) | ¥357.4 | ¥6.77 |
| Output (per 1M tokens) | ¥1,072.2 | ¥25.38 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥894 | ¥19 |
| Context window | 500,000 tokens | 260,000 tokens |
| Release date | 8/12/2026 | 9/8/2026 |
| Input modalities | text, image, file | text |
| Arena · overall | #49 · ELO 1,461 | Unranked |
| Arena · Japanese | Unranked | Unranked |
| Arena · coding | #45 · ELO 1,511 | Unranked |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Mercury 2.5: ¥25.38 per 1M output tokens, 98% less than Grok 4.6.
- For long documents, Grok 4.6: a 500,000-token context window against 260,000 for Mercury 2.5.
- 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.
Grok 4.6
The word "strawberry" consists of the following letters in order:
s-t-r-a-w-b-e-r-r-y
Checking each one:
- s: not r
- t: not r
- r: yes (count = 1)
- a: not r
- w: not r
- b: not r
- e: not r
- r: yes (count = 2)
- r: yes (count = 3)
- y: not r
There are exactly 3 r's.
Final answer: 3
3.9s451 output tokens
Mercury 2.5
To determine the number of 'r's in the word "strawberry", we can examine each letter in sequence:
1. **s** - Not 'r'
2. **t** - Not 'r'
3. **r** - First 'r' found
4. **a** - Not 'r'
5. **w** - Not 'r'
6. **b** - Not 'r'
7. **e** - Not 'r'
8. **r** - Second 'r' found
9. **r** - Third 'r' found
10. **y** - Not 'r'
Counting these occurrences, there are **3** 'r's in "strawberry".
1.8s968 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…
Grok 4.6
**The error happens because `users` is `undefined` when `.map()` is called.**
`UserList` destructures `{ users }` from its props. If the parent doesn't pass a `users` prop (or passes `undefined`/`null`), `users` is `undefined` and `undefined.map` throws.
This is extremely common when:
- Data is loaded asynchronously (initial render happens before the fetch finishes).
- The parent component forgets to pass the prop or uses a different name.
- The component is rendered before the data is ready (e.g. in a loading state).
### Quick fixes
**1. Default to an empty array (recommended)**
```jsx
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => (
<li key={us…
20.3s598 output tokens
Mercury 2.5
This error occurs because the `users` prop is `undefined` when the component renders. Since the code calls `.map()` on `users`, JavaScript throws a TypeError when `users` is not an array.
Here is how to fix it:
1. **Set a Default Value**
Update the function signature to default `users` to an empty array if it is not provided:
```javascript
function UserList({ users = [] }) {
// ...
}
```
2. **Add a Conditional Check**
If `users` might be null or undefined during data loading, guard the map operation:
```javascript
{users && users.map(user => <li key={user.id}>{user.name}</li>)}
```
3. **Verify Parent Props**
Ensure the parent component pas…
2.4s1028 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):…
Grok 4.6
Here is a focused review of the function, followed by a cleaned-up version.
## Issues
**Imports inside the function**
`requests` and `time` should live at module level. Importing on every call is slower, hides dependencies, and is harder to mock in tests.
**Bare `except:`**
This swallows `KeyboardInterrupt`, `SystemExit`, and programming errors. Catch `requests.RequestException` (network/timeout/HTTP adapter errors) and JSON/`KeyError`/`TypeError` separately.
**Retrying the wrong things**
A 404 or 400 will never succeed on retry. Retry transient failures (timeouts, connection errors, 429, 5xx). Fail fast on most 4xx responses.
**Sleep after the last attempt**
On the final failur…
27.9s1770 output tokens
Mercury 2.5
Here is a review of the function with suggestions for improvement.
### Key Observations
1. **Imports:** Libraries should be imported at the module level, not inside functions.
2. **Exception Handling:** Bare `except:` clauses catch system exits and interrupts. Use specific exceptions like `requests.exceptions.RequestException`.
3. **Logic & Pythonicity:**
* Avoid `== True`; rely on truthiness or `item.get("active")`.
* List comprehensions are more concise and efficient than manual appending.
4. **Retry Strategy:** Implement exponential backoff instead of fixed sleeps, and avoid sleeping after the final failed attempt.
5. **Documentation:** Add type hints and a docstring fo…
4.6s1999 output tokens
Frequently asked questions
- Which is cheaper, Grok 4.6 or Mercury 2.5?
- Per 1M output tokens, Grok 4.6 is ¥1,072.2 and Mercury 2.5 is ¥25.38 on FastMetal (yen, before tax), so Mercury 2.5 is cheaper.
- How do the context windows of Grok 4.6 and Mercury 2.5 compare?
- Grok 4.6 takes 500,000 tokens; Mercury 2.5 takes 260,000.
- Can I use Grok 4.6 and Mercury 2.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "grok-4.6" or "mercury-2.5" 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 Grok 4.6 and Mercury 2.5 from the browser chat and the API. No monthly fee.