FastMetal

Model comparison

GPT-5.6 Sol vs Kimi K3.1 Pro

Pricing, context window and real answers (October 2026)

GPT-5.6 Sol (OpenAI) and Kimi K3.1 Pro (Moonshot), 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

openai logoGPT-5.6 Solmoonshotai logoKimi K3.1 Pro
ProviderOpenAIMoonshot
Input (per 1M tokens)$4.40$2.11
Output (per 1M tokens)$22.00$10.55
Typical cost (1,000 in + 500 out tokens × 1,000 calls)$15.40$7.39
Context window1,050,000 tokens1,048,576 tokens
Release date7/9/202610/23/2026
Input modalitiesfile, image, texttext, image, video
Throughput (p50)205 tokens/s (n=27)—
Arena · overall#21 · ELO 1,485Unranked
Arena · Japanese#12 · ELO 1,497Unranked
Arena · coding#17 · ELO 1,534Unranked

Prices are FastMetal's rates, before tax.

Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-10-22; category names mapped and ratings rounded by FastMetal.

Which should you pick?

  • On price, Kimi K3.1 Pro: $10.55 per 1M output tokens, 52% less than GPT-5.6 Sol.
  • For long documents, GPT-5.6 Sol: a 1,050,000-token context window against 1,048,576 for Kimi K3.1 Pro.
  • 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-5.6 Sol

“strawberry” can be split into letters: s, t, **r**, a, w, b, e, **r**, **r**, y The letter **r** appears **3 times**.
3.0s78 output tokens

Kimi K3.1 Pro

There are **3** ‘r’s in **“strawberry.”** 1. Write out each letter: **s – t – r – a – w – b – e – r – r – y** 2. Locate the ‘r’s: positions **3, 8, and 9**. 3. Count them: **1 + 1 + 1 = 3**.
11.3s

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-5.6 Sol

The error occurs because `users` is `undefined` when `UserList` renders, so JavaScript cannot call `.map()` on it. This often happens when data is loaded asynchronously or the parent does not pass the prop. ### Fix options **1. Give `users` a default value:** ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => ( <li key={user.id}>{user.name}</li> ))} </ul> ); } ``` Note that this handles `undefined`, but not an explicitly passed `null`. **2. Handle missing or invalid data explicitly:** ```jsx function UserList({ users }) { if (!Array.isArray(users)) { return <p>No users available.</p>; } return ( <ul> {users.m…
7.1s395 output tokens

Kimi K3.1 Pro

## What's causing the error The error means `users` is `undefined` when the component renders, and you can't call `.map()` on `undefined`. The component itself is fine — the problem is that whatever renders `<UserList />` either isn't passing the prop, or is passing a value that isn't an array yet. The most common cause is **async data fetching**: the parent renders `UserList` before the data has loaded. ```jsx function App() { const [users, setUsers] = useState(); // ❌ undefined on first render useEffect(() => { fetch('/api/users') .then(res => res.json()) .then(setUsers); }, []); return <UserList users={users} />; // users is undefined here initially } ``` On…
36.3s

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-5.6 Sol

### Issues and suggested improvements - Move imports to module scope. - Avoid bare `except:`; it catches programming errors and interrupts such as `KeyboardInterrupt`. - Use `response.raise_for_status()` instead of manually checking only for `200`; other 2xx responses may also be valid. - Retry only transient failures, such as timeouts, connection errors, `429`, and selected `5xx` responses. Retrying most `4xx` errors is not useful. - Use exponential backoff rather than a fixed delay. - Avoid sleeping after the final failed attempt. - Replace `item["active"] == True` with `item.get("active") is True`. - Use a list comprehension for the transformation. - Add type hints and validate arguments…
33.1s1646 output tokens

Kimi K3.1 Pro

The timeout and bounded retry loop are good starting points. The biggest issue is that failures—and even programming errors—are silently converted into retries and then `[]`. ### Suggested improvements - **Avoid bare `except:`**. It catches `KeyboardInterrupt`, `KeyError`, JSON/schema errors, and other bugs. Retry only expected transient network failures; let malformed responses fail visibly. - **Use a deliberate retry policy**. Retrying `401`, `403`, or `404` usually wastes time. Retry only transient statuses, use exponential backoff, and avoid sleeping after the final attempt. - **Do not use `[]` for both failure and no results**. Prefer raising the final exception so callers can disting…
560.2s

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Frequently asked questions

Which is cheaper, GPT-5.6 Sol or Kimi K3.1 Pro?
Per 1M output tokens, GPT-5.6 Sol is $22.00 and Kimi K3.1 Pro is $10.55 on FastMetal (US dollars, before tax), so Kimi K3.1 Pro is cheaper.
How do the context windows of GPT-5.6 Sol and Kimi K3.1 Pro compare?
GPT-5.6 Sol takes 1,050,000 tokens; Kimi K3.1 Pro takes 1,048,576.
Can I use GPT-5.6 Sol and Kimi K3.1 Pro with the same API key?
Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-5.6-sol" or "kimi-k3.1-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 GPT-5.6 Sol and Kimi K3.1 Pro from the browser chat and the API. No monthly fee.

Create a free accountTry GPT-5.6 Sol in chatTry Kimi K3.1 Pro in chat

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