Claude Sonnet 5 vs DeepSeek V4 Pro
Pricing, context window and real answers (August 2026)
Claude Sonnet 5 (Anthropic) and DeepSeek V4 Pro (DeepSeek), 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 Sonnet 5 |  DeepSeek V4 Pro | |
|---|---|---|
| Provider | Anthropic | DeepSeek |
| Input (per 1M tokens) | ¥357.4 | ¥341.32 |
| Output (per 1M tokens) | ¥1,787 | ¥684.42 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥1,251 | ¥684 |
| Context window | 1,000,000 tokens | 1,048,576 tokens |
| Release date | 6/30/2026 | 4/24/2026 |
| Input modalities | text, image, file | text |
| Arena · overall | #44 · ELO 1,460 | #49 · ELO 1,457 |
| Arena · Japanese | #14 · ELO 1,469 | #18 · ELO 1,462 |
| Arena · coding | #19 · ELO 1,522 | #54 · ELO 1,502 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, DeepSeek V4 Pro: ¥684.42 per 1M output tokens, 62% less than Claude Sonnet 5.
- On the Overall arena board, Claude Sonnet 5 ranks higher (#44; DeepSeek V4 Pro is #49).
- On the Japanese arena board, Claude Sonnet 5 ranks higher (#14; DeepSeek V4 Pro is #18).
- On the Coding arena board, Claude Sonnet 5 ranks higher (#19; DeepSeek V4 Pro is #54).
- For long documents, DeepSeek V4 Pro: a 1,048,576-token context window against 1,000,000 for Claude Sonnet 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 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
DeepSeek V4 Pro
The word is "strawberry". Let's count the occurrences of the letter 'r' step by step:
1. Write the word: s t r a w b e r r y
2. Examine each character:
- s: not an 'r'
- t: not an 'r'
- r: is an 'r' → count 1
- a: not an 'r'
- w: not an 'r'
- b: not an 'r'
- e: not an 'r'
- r: is an 'r' → count 2
- r: is an 'r' → count 3
- y: not an 'r'
3. Total number of 'r's = 3.
Therefore, there are **3** 'r's in "strawberry".
7.3s1136 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 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
DeepSeek V4 Pro
The error is occurring because `users` is `undefined` when the component renders, and you're trying to call `.map()` on it. This typically happens when the data hasn't been loaded yet or wasn't passed correctly to the component.
## Here are several ways to fix this:
### 1. **Add a default value with empty array (Simplest fix)**
```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 <div>No users found</div>;
}
return (
<ul>
{users.map(user => <li key={user.id}>{user.name}<…
6.9s442 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 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
DeepSeek V4 Pro
Here’s a review of your `get_data` function, highlighting issues and suggesting improvements.
## Overall Observations
- The function works but has several readability, robustness, and maintainability issues.
- Imports are inside the function, bare `except` hides errors, and the filtering logic is not Pythonic.
- No type hints or docstring, making it harder to use and understand.
## Specific Improvements
### 1. Move Imports to the Top of the Module
**Why:** Imports inside a function are executed every time the function is called, which is slightly slower and violates PEP 8 style guidelines.
**Before:**
```python
def get_data(url, retries=3):
import requests
import time
# ...
`…
40.5s2277 output tokens
Frequently asked questions
- Which is cheaper, Claude Sonnet 5 or DeepSeek V4 Pro?
- Per 1M output tokens, Claude Sonnet 5 is ¥1,787 and DeepSeek V4 Pro is ¥684.42 on FastMetal (yen, before tax), so DeepSeek V4 Pro is cheaper.
- How do the context windows of Claude Sonnet 5 and DeepSeek V4 Pro compare?
- Claude Sonnet 5 takes 1,000,000 tokens; DeepSeek V4 Pro takes 1,048,576.
- Which ranks higher, Claude Sonnet 5 or DeepSeek V4 Pro?
- Claude Sonnet 5 ranks higher on the public arena (Claude Sonnet 5 #14, DeepSeek V4 Pro #18). Ranks move as the leaderboard updates.
- Can I use Claude Sonnet 5 and DeepSeek V4 Pro with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-sonnet-5" or "deepseek-v4-pro" 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 Sonnet 5 and DeepSeek V4 Pro from the browser chat and the API. No monthly fee.