Gemini 3.1 Pro Preview vs Gemini 3.8 Flash
Pricing, context window and real answers (September 2026)
Gemini 3.1 Pro Preview (Google) and Gemini 3.8 Flash (Google), 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
 Gemini 3.1 Pro Preview | Gemini 3.8 Flash | |
|---|---|---|
| Provider | ||
| Input (per 1M tokens) | ¥357.4 | ¥128.83 |
| Output (per 1M tokens) | ¥2,144.4 | ¥644.15 |
| Typical cost (1,000 in + 500 out tokens × 1,000 calls) | ¥1,430 | ¥451 |
| Context window | 1,048,576 tokens | 1,048,576 tokens |
| Release date | 2/19/2026 | 9/2/2026 |
| Input modalities | audio, file, image, text, video | text, image, video, file, audio |
| Throughput (p50) | — | — |
| Arena · overall | #15 · ELO 1,487 | #9 · ELO 1,493 |
| Arena · Japanese | #9 · ELO 1,494 | Unranked |
| Arena · coding | #28 · ELO 1,520 | #10 · ELO 1,535 |
Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.
Which should you pick?
- On price, Gemini 3.8 Flash: ¥644.15 per 1M output tokens, 70% less than Gemini 3.1 Pro Preview.
- On the Overall arena board, Gemini 3.8 Flash ranks higher (#9; Gemini 3.1 Pro Preview is #15).
- On the Coding arena board, Gemini 3.8 Flash ranks higher (#10; Gemini 3.1 Pro Preview is #28).
- 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.
Gemini 3.1 Pro Preview
There are **3** 'r's in the word 'strawberry'.
Here is the step-by-step breakdown of the spelling:
1. **s** - not an 'r'
2. **t** - not an 'r'
3. **r** - **1st 'r'**
4. **a** - not an 'r'
5. **w** - not an 'r'
6. **b** - not an 'r'
7. **e** - not an 'r'
8. **r** - **2nd 'r'**
9. **r** - **3rd 'r'**
10. **y** - not an 'r'
Therefore, the total count is 3.
5.3s503 output tokens
Gemini 3.8 Flash
There are **3** 'r's in the word "strawberry".
Here is the step-by-step breakdown:
1. **Break the word into its individual letters:**
* **s** (1st letter)
* **t** (2nd letter)
* **r** (3rd letter) — **1st 'r'**
* **a** (4th letter)
* **w** (5th letter)
* **b** (6th letter)
* **e** (7th letter)
* **r** (8th letter) — **2nd 'r'**
* **r** (9th letter) — **3rd 'r'**
* **y** (10th letter)
2. **Count the occurrences:**
* One 'r' is in the first syllable: "st**r**aw"
* Two 'r's are in the second syllable: "be**rr**y"
Total: **3**
3.9s562 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…
Gemini 3.1 Pro Preview
### The Cause
This error occurs because the `users` prop being passed to your `UserList` component is currently `undefined`.
In JavaScript, you can only use the `.map()` method on arrays. Because `users` is `undefined` (often due to data not finishing an API fetch yet, or the parent component forgetting to pass the prop), Node/React throws an error when it tries to read `.map`.
### How to Fix It
You can fix this in a few different ways, depending on how you want your application to behave.
#### Fix 1: Assign a Default Value (Recommended)
The cleanest way to handle this is to assign a default empty array to `users` in your component's parameters. If `users` is undefined, it defaults to…
13.2s1511 output tokens
Gemini 3.8 Flash
### The Cause
This error occurs because the `users` prop is `undefined` when the component renders, and JavaScript cannot call `.map()` on `undefined`.
This typically happens in two common scenarios:
1. **Asynchronous data fetching:** The parent component fetches `users` from an API. On the initial render, the data hasn't arrived yet, so `users` defaults to `undefined`.
2. **Missing prop:** The parent component forgot to pass `users` (e.g., `<UserList />` instead of `<UserList users={data} />`).
---
### How to Fix It
Here are the most common ways to resolve this:
#### Option 1: Provide a default parameter (Recommended)
Set a default value of an empty array (`[]`) for `users`. If `users…
7.1s1003 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):…
Gemini 3.1 Pro Preview
Here is a review of your function. While the original code works, there are several areas where it can be improved regarding **best practices**, **readability**, and **performance**.
### 1. Refactored Code
Here is the improved version of your function. I will explain the specific changes below.
```python
import time
import requests
import logging
from typing import Any
# Optional: Set up a logger
logger = logging.getLogger(__name__)
def get_data(url: str, retries: int = 3, delay: int = 2, timeout: int = 10) -> list[dict[str, Any]]:
"""
Fetches JSON data from a URL and extracts active items.
Args:
url: The API endpoint to fetch data from.
retries: Number o…
23.6s3094 output tokens
Gemini 3.8 Flash
Here is a code review of your function, broken down by issue category, followed by refactored versions.
---
### Key Issues & Areas for Improvement
#### 1. Correctness & Error Handling
* **Bare `except:` clause:** Catching all exceptions with a bare `except:` is dangerous. It suppresses system exits (`KeyboardInterrupt`, `SystemExit`) and masks programming bugs (like `KeyError` or `NameError`). You should catch specific exceptions, primarily `requests.RequestException`.
* **Silent failure returning `[]`:** If all retries fail, returning an empty list makes it impossible for the caller to distinguish between *"the API returned 0 active items"* and *"the network is completely down"*. It is u…
15.1s2139 output tokens
Frequently asked questions
- Which is cheaper, Gemini 3.1 Pro Preview or Gemini 3.8 Flash?
- Per 1M output tokens, Gemini 3.1 Pro Preview is ¥2,144.4 and Gemini 3.8 Flash is ¥644.15 on FastMetal (yen, before tax), so Gemini 3.8 Flash is cheaper.
- How do the context windows of Gemini 3.1 Pro Preview and Gemini 3.8 Flash compare?
- Gemini 3.1 Pro Preview takes 1,048,576 tokens; Gemini 3.8 Flash takes 1,048,576.
- Which ranks higher, Gemini 3.1 Pro Preview or Gemini 3.8 Flash?
- They share the same public arena rank (#9). Ranks move as the leaderboard updates.
- Can I use Gemini 3.1 Pro Preview and Gemini 3.8 Flash with the same API key?
- Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gemini-3.1-pro-preview" or "gemini-3.8-flash" 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 Gemini 3.1 Pro Preview and Gemini 3.8 Flash from the browser chat and the API. No monthly fee.