gpt-oss-120b vs Grok 4.5
Pricing, context window and real answers (August 2026)
gpt-oss-120b (OpenAI) 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
 gpt-oss-120b |  Grok 4.5 | |
|---|---|---|
| Provider | OpenAI | xAI |
| Input (per 1M tokens) | ¥16 | ¥357.4 |
| Output (per 1M tokens) | ¥79 | ¥1,072.2 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥56 | ¥894 |
| Context window | 131,072 tokens | 500,000 tokens |
| Release date | 8/5/2025 | 7/8/2026 |
| Input modalities | text | text, image, file |
| Arena · overall | #186 · ELO 1,352 | #35 · ELO 1,468 |
| Arena · Japanese | #123 · ELO 1,320 | Unranked |
| Arena · coding | #190 · ELO 1,390 | #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, gpt-oss-120b: ¥79 per 1M output tokens, 93% less than Grok 4.5.
- On the Overall arena board, Grok 4.5 ranks higher (#35; gpt-oss-120b is #186).
- On the Coding arena board, Grok 4.5 ranks higher (#28; gpt-oss-120b is #190).
- For long documents, Grok 4.5: a 500,000-token context window against 131,072 for gpt-oss-120b.
- 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.
gpt-oss-120b
**Step‑by‑step count of the letter “r” in the word “strawberry”**
1. Write out the word with each letter in order, labeling its position:
| Position | Letter |
|----------|--------|
| 1 | s |
| 2 | t |
| 3 | **r** |
| 4 | a |
| 5 | w |
| 6 | b |
| 7 | e |
| 8 | **r** |
| 9 | **r** |
|10 | y |
2. Scan the list and mark every occurrence of the letter **r**.
- Position 3 → r (first occurrence)
- Position 8 → r (second occurrence)
- Position 9 → r (third occurrence)
3. Count the marked entries: there are **3** marked positions.
**Result:** The word “strawberry” contains **3** occurrences of the letter **r**…
1.7s332 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…
gpt-oss-120b
### Why the `map` can’t be called
`Array.prototype.map` is a method that exists only on **arrays** (or array‑like objects).
When you see
```
TypeError: Cannot read properties of undefined (reading 'map')
at UserList (...)
```
it means that the variable you think is an array – `users` in this case – is actually **`undefined`** (or `null`).
React is trying to evaluate this line:
```jsx
{users.map(user => <li key={user.id}>{user.name}</li>)}
```
and it crashes because you can’t read `.map` from `undefined`.
---
## Common reasons `users` ends up undefined
| Reason | Typical scenario | How it shows up |
|--------|------------------|-----------------|
| **Prop not passed** | `<Use…
7.3s1610 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):…
gpt-oss-120b
Below is a **step‑by‑step review** of the original `get_data` implementation followed by a **refactored version** that addresses readability, performance, and modern Python best‑practice concerns.
---
## 1. What the original function does
```python
def get_data(url, retries=3):
import requests
import time
for i in range(retries):
try:
r = requests.get(url, timeout=10)
if r.status_code == 200:
data = r.json()
result = []
for item in data:
if item["active"] == True:
result.append({"name": item["name"], "id": item["id"]})
return result…
14.4s3132 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, gpt-oss-120b or Grok 4.5?
- Per 1M output tokens, gpt-oss-120b is ¥79 and Grok 4.5 is ¥1,072.2 on FastMetal (yen, before tax), so gpt-oss-120b is cheaper.
- How do the context windows of gpt-oss-120b and Grok 4.5 compare?
- gpt-oss-120b takes 131,072 tokens; Grok 4.5 takes 500,000.
- Which ranks higher, gpt-oss-120b or Grok 4.5?
- Grok 4.5 ranks higher on the public arena (gpt-oss-120b #123, Grok 4.5 #35). Ranks move as the leaderboard updates.
- Can I use gpt-oss-120b and Grok 4.5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-oss-120b" 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 gpt-oss-120b and Grok 4.5 from the browser chat and the API. No monthly fee.