Claude Haiku 4.5 vs Claude Sonnet 5
Pricing, context window and real answers (August 2026)
Claude Haiku 4.5 (Anthropic) and Claude Sonnet 5 (Anthropic), 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 | Claude Sonnet 5 | |
|---|---|---|
| Provider | Anthropic | Anthropic |
| Input (per 1M tokens) | ¥184.8 | ¥357.4 |
| Output (per 1M tokens) | ¥924 | ¥1,787 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥647 | ¥1,251 |
| Context window | 200,000 tokens | 1,000,000 tokens |
| Release date | 10/15/2025 | 6/30/2026 |
| Input modalities | image, text | text, image, file |
| Arena · overall | #120 · ELO 1,412 | #44 · ELO 1,460 |
| Arena · Japanese | #99 · ELO 1,355 | #14 · ELO 1,469 |
| Arena · coding | #86 · ELO 1,479 | #19 · ELO 1,522 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Claude Haiku 4.5: ¥924 per 1M output tokens, 48% less than Claude Sonnet 5.
- On the Overall arena board, Claude Sonnet 5 ranks higher (#44; Claude Haiku 4.5 is #120).
- On the Japanese arena board, Claude Sonnet 5 ranks higher (#14; Claude Haiku 4.5 is #99).
- On the Coding arena board, Claude Sonnet 5 ranks higher (#19; Claude Haiku 4.5 is #86).
- For long documents, Claude Sonnet 5: a 1,000,000-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
Claude Sonnet 5
# Counting 'r's in "strawberry"
**Step 1: Spell out the word letter by letter**
s - t - r - a - w - b - e - r - r - y
**Step 2: Number each letter position**
| Position | Letter |
|----------|--------|
| 1 | s |
| 2 | t |
| 3 | **r** |
| 4 | a |
| 5 | w |
| 6 | b |
| 7 | e |
| 8 | **r** |
| 9 | **r** |
| 10 | y |
**Step 3: Identify and count the 'r's**
- Position 3: **r** ✓ (1st r)
- Position 8: **r** ✓ (2nd r)
- Position 9: **r** ✓ (3rd r)
**Answer: There are 3 r's in "strawberry"**
5.9s405 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
Claude Sonnet 5
# Root Cause
The `UserList` component receives `users` as a prop, but at the time it's rendered, `users` is `undefined` — not an empty array, but literally missing. When your code tries to call `.map()` on `undefined`, JavaScript throws that `TypeError`.
This typically happens when:
- The parent component hasn't fetched the data yet (e.g., an API call is still in progress)
- The prop name doesn't match what's being passed down (typo)
- The data source (API/state) genuinely returns `undefined` in some case
# Fixes
**1. Add a default prop value (quick fix)**
```jsx
function UserList({ users = [] }) {
return (
<ul>
{users.map(user => <li key={user.id}>{user.name}</li>)}
</u…
8.8s750 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
Claude Sonnet 5
## Review of `get_data` Function
Here's an improved version followed by an explanation of the changes:
```python
import logging
import time
from typing import Any
import requests
logger = logging.getLogger(__name__)
def get_data(
url: str,
retries: int = 3,
timeout: float = 10.0,
backoff_factor: float = 2.0,
) -> list[dict[str, Any]]:
"""
Fetch active items from the given URL.
Args:
url: The endpoint to fetch data from.
retries: Number of attempts before giving up.
timeout: Request timeout in seconds.
backoff_factor: Multiplier for exponential backoff between retries.
Returns:
A list of dicts with "name" and "id"…
14.0s1299 output tokens
Frequently asked questions
- Which is cheaper, Claude Haiku 4.5 or Claude Sonnet 5?
- Per 1M output tokens, Claude Haiku 4.5 is ¥924 and Claude Sonnet 5 is ¥1,787 on FastMetal (yen, before tax), so Claude Haiku 4.5 is cheaper.
- How do the context windows of Claude Haiku 4.5 and Claude Sonnet 5 compare?
- Claude Haiku 4.5 takes 200,000 tokens; Claude Sonnet 5 takes 1,000,000.
- Which ranks higher, Claude Haiku 4.5 or Claude Sonnet 5?
- Claude Sonnet 5 ranks higher on the public arena (Claude Haiku 4.5 #99, Claude Sonnet 5 #14). Ranks move as the leaderboard updates.
- Can I use Claude Haiku 4.5 and Claude Sonnet 5 with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-haiku-4-5" or "anthropic-claude-sonnet-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 Haiku 4.5 and Claude Sonnet 5 from the browser chat and the API. No monthly fee.