FastMetal

Model comparison

GPT-6 Luna vs GPT-6 Sol

Pricing, context window and real answers (September 2026)

GPT-6 Luna (OpenAI) and GPT-6 Sol (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

openai logoGPT-6 Lunaopenai logoGPT-6 Sol
ProviderOpenAIOpenAI
Input (per 1M tokens)¥17.87¥357.4
Output (per 1M tokens)¥89.35¥1,787
Typical cost (1,000 in + 500 out tokens × 1,000 calls)¥63¥1,251
Context window1,050,000 tokens1,050,000 tokens
Release date9/22/20269/22/2026
Input modalitiesfile, image, textfile, image, text
Throughput (p50)——
Arena · overallUnrankedUnranked
Arena · JapaneseUnrankedUnranked
Arena · codingUnrankedUnranked

Prices are FastMetal's yen rates before tax. Arena ranks are as of the latest leaderboard scrape.

Which should you pick?

  • On price, GPT-6 Luna: ¥89.35 per 1M output tokens, 95% less than GPT-6 Sol.
  • 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-6 Luna

In **“strawberry”**, the letter **r** appears at positions 3, 8, and 9. So there are **3** “r”s.
2.7s94 output tokens

GPT-6 Sol

“Strawberry” is spelled **s-t-r-a-w-b-e-r-r-y**. There’s one **r** near the beginning and two near the end, for a total of **3**.
2.7s76 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…

GPT-6 Luna

`users` is `undefined` when `UserList` renders, so calling `users.map(...)` throws. This often happens because the parent didn’t pass the prop or because data hasn’t loaded yet. If an empty list is acceptable until the data arrives, provide a default: ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => ( <li key={user.id}>{user.name}</li> ))} </ul> ); } ``` Also check that the parent passes `users`: ```jsx <UserList users={users} /> ``` If `users` is loaded asynchronously, initialize it as an array: ```jsx const [users, setUsers] = useState([]); ``` If `null` is also possible, normalize it before mapping, for example `(users ?? […
3.8s289 output tokens

GPT-6 Sol

`users` is `undefined` when `UserList` renders, so calling `users.map(...)` throws the error. The component needs an array, but its parent may not be passing `users`, or the data may not have loaded yet. You can default it to an empty array: ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => <li key={user.id}>{user.name}</li>)} </ul> ); } ``` Also check the parent component to make sure it passes an array: ```jsx <UserList users={users} /> ``` If `users` comes from an API, initialize its state as `[]` or show a loading state until the data arrives.
2.2s161 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):…

GPT-6 Luna

Key improvements: - Move imports to module scope. - Catch `requests.RequestException` instead of using a bare `except`; the current handler can hide programming errors as well as network failures. - Call `raise_for_status()` so unsuccessful HTTP responses are handled explicitly. - Use a list comprehension instead of building the result manually. - Replace `item["active"] == True` with `item.get("active") is True` if the field is expected to be the Boolean `True`. - Add backoff between attempts. A fixed two-second delay can make retries slower than necessary. - Decide whether failures should raise an exception or return `[]`. Returning `[]` makes a failed request indistinguishable from a suc…
16.5s1713 output tokens

GPT-6 Sol

The main issues are the bare `except`, which hides errors such as malformed JSON, and retrying every non-200 response, including client errors that usually won’t improve with another attempt. The function also sleeps after its final attempt. ```python import time import requests def get_data(url, retries=3): if retries < 1: raise ValueError("retries must be at least 1") for attempt in range(retries): try: response = requests.get(url, timeout=10) except requests.RequestException: if attempt == retries - 1: raise else: # Retry rate limits and server errors, but not other client errors.…
10.3s814 output tokens

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Frequently asked questions

Which is cheaper, GPT-6 Luna or GPT-6 Sol?
Per 1M output tokens, GPT-6 Luna is ¥89.35 and GPT-6 Sol is ¥1,787 on FastMetal (yen, before tax), so GPT-6 Luna is cheaper.
How do the context windows of GPT-6 Luna and GPT-6 Sol compare?
GPT-6 Luna takes 1,050,000 tokens; GPT-6 Sol takes 1,050,000.
Can I use GPT-6 Luna and GPT-6 Sol with the same API key?
Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-6-luna" or "gpt-6-sol" 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-6 Luna and GPT-6 Sol from the browser chat and the API. No monthly fee.

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