Claude Haiku 4.5 vs GPT-5.6 Luna
Pricing, context window and real answers (August 2026)
Claude Haiku 4.5 (Anthropic) and GPT-5.6 Luna (OpenAI), 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 Haiku 4.5 |  GPT-5.6 Luna | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input (per 1M tokens) | ¥184.8 | ¥35.74 |
| Output (per 1M tokens) | ¥924 | ¥214.44 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥647 | ¥143 |
| Context window | 200,000 tokens | 1,050,000 tokens |
| Release date | 10/15/2025 | 7/9/2026 |
| Input modalities | image, text | file, image, text |
| Arena · overall | #129 · ELO 1,413 | #63 · ELO 1,452 |
| Arena · Japanese | #112 · ELO 1,357 | #36 · ELO 1,444 |
| Arena · coding | #95 · ELO 1,480 | #69 · ELO 1,496 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, GPT-5.6 Luna: ¥214.44 per 1M output tokens, 77% less than Claude Haiku 4.5.
- On the Overall arena board, GPT-5.6 Luna ranks higher (#63; Claude Haiku 4.5 is #129).
- On the Japanese arena board, GPT-5.6 Luna ranks higher (#36; Claude Haiku 4.5 is #112).
- On the Coding arena board, GPT-5.6 Luna ranks higher (#69; Claude Haiku 4.5 is #95).
- For long documents, GPT-5.6 Luna: a 1,050,000-token context window against 200,000 for Claude Haiku 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 Haiku 4.5
# Counting the 'r's in "strawberry"
Let me go through each letter in the word "strawberry":
1. **s** - not an 'r'
2. **t** - not an 'r'
3. **r** - this is an 'r' ✓ (1st)
4. **a** - not an 'r'
5. **w** - not an 'r'
6. **b** - not an 'r'
7. **e** - not an 'r'
8. **r** - this is an 'r' ✓ (2nd)
9. **r** - this is an 'r' ✓ (3rd)
10. **y** - not an 'r'
**Answer: There are 3 'r's in "strawberry"**
The 'r's appear in positions 3, 8, and 9 of the word.
4.1s228 output tokens
GPT-5.6 Luna
The word **“strawberry”** is spelled:
**s – t – r – a – w – b – e – r – r – y**
The letter **“r”** appears at positions **3, 8, and 9**.
**Answer: 3**
3.0s120 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 Haiku 4.5
# TypeError: Cannot read properties of undefined (reading 'map')
This error occurs because `users` is `undefined` when the component renders. You're trying to call `.map()` on `undefined`, which doesn't have that method.
## Common Causes
1. **Parent component didn't pass the `users` prop**
2. **Async data hasn't loaded yet**
3. **Props passed incorrectly**
## Solutions
### 1. **Provide a Default Value** (Recommended)
```javascript
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => <li key={user.id}>{user.name}</li>)}
</ul>
);
}
```
### 2. **Add a Conditional Check**
```javascript
function UserList({ users }) {
if (!users) {
return <p>No users a…
3.9s671 output tokens
GPT-5.6 Luna
`users` is `undefined` when `UserList` renders, so calling `.map()` on it fails. `.map()` only exists on arrays.
Common causes include:
- The parent does not pass a `users` prop.
- The prop name differs, such as `userList` instead of `users`.
- Users are loaded asynchronously and are initially undefined.
- The API response has a different shape, such as `{ data: [...] }`.
### Provide a default value
```jsx
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => (
<li key={user.id}>{user.name}</li>
))}
</ul>
);
}
```
The parent should pass an array:
```jsx
<UserList users={users} />
```
If the list comes from state, initialize it as an empty…
4.8s507 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 Haiku 4.5
# Code Review and Improvements
## Issues Found
1. **Bare `except`** - Catches all exceptions, hiding bugs
2. **Imports inside function** - Should be at module level
3. **Redundant comparison** - `== True` is unnecessary
4. **No logging** - Hard to debug failures
5. **Magic numbers** - Hardcoded timeout and sleep values
6. **Inefficient retries** - Doesn't retry on 200 with parsing errors
7. **Poor variable names** - `r`, `i` are unclear
8. **No type hints** - Reduces code clarity
## Improved Version
```python
import logging
import requests
import time
from typing import Optional
from requests.exceptions import RequestException
logger = logging.getLogger(__name__)
def get_data(
url:…
5.7s988 output tokens
GPT-5.6 Luna
### Main issues
- Imports should be at module level, not inside the function.
- A bare `except:` catches everything, including programming errors and `KeyboardInterrupt`.
- The function sleeps even after the final failed attempt.
- It retries all HTTP statuses, including permanent errors such as `404`.
- `status_code == 200` excludes other successful `2xx` responses.
- `if item["active"] == True` should generally be `if item.get("active") is True`.
- A `requests.Session` can reuse connections and improve performance.
- Returning `[]` for every failure makes it impossible to distinguish “no active items” from “request failed.”
- Retries should generally use backoff rather than a fixed delay.…
23.3s1978 output tokens
Frequently asked questions
- Which is cheaper, Claude Haiku 4.5 or GPT-5.6 Luna?
- Per 1M output tokens, Claude Haiku 4.5 is ¥924 and GPT-5.6 Luna is ¥214.44 on FastMetal (yen, before tax), so GPT-5.6 Luna is cheaper.
- How do the context windows of Claude Haiku 4.5 and GPT-5.6 Luna compare?
- Claude Haiku 4.5 takes 200,000 tokens; GPT-5.6 Luna takes 1,050,000.
- Which ranks higher, Claude Haiku 4.5 or GPT-5.6 Luna?
- GPT-5.6 Luna ranks higher on the public arena (Claude Haiku 4.5 #112, GPT-5.6 Luna #36). Ranks move as the leaderboard updates.
- Can I use Claude Haiku 4.5 and GPT-5.6 Luna with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-haiku-4-5" or "gpt-5.6-luna" 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 Haiku 4.5 and GPT-5.6 Luna from the browser chat and the API. No monthly fee.