FastMetal

Model comparison

Claude Haiku 5.5 vs GPT-6 Luna

Pricing, context window and real answers (October 2026)

Claude Haiku 5.5 (Anthropic) and GPT-6 Luna (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

anthropic logoClaude Haiku 5.5openai logoGPT-6 Luna
ProviderAnthropicOpenAI
Input (per 1M tokens)$0.1055$0.1055
Output (per 1M tokens)$0.5275$0.5275
Typical cost (1,000 in + 500 out tokens × 1,000 calls)$0.3693$0.3693
Context window1,000,000 tokens1,050,000 tokens
Release date10/7/20269/22/2026
Input modalitiestext, image, filefile, image, text
Throughput (p50)——
Arena · overallUnranked#90 · ELO 1,443
Arena · JapaneseUnranked#80 · ELO 1,406
Arena · codingUnranked#55 · ELO 1,512

Prices are FastMetal's rates, before tax.

Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-10-02; category names mapped and ratings rounded by FastMetal.

Which should you pick?

  • Output pricing is identical ($0.5275 per 1M tokens).
  • For long documents, GPT-6 Luna: a 1,050,000-token context window against 1,000,000 for Claude Haiku 5.5.
  • 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 5.5

There are **3** r's in "strawberry." 1. **Spell out the word:** s, t, r, a, w, b, e, r, r, y 2. **Go through each letter and count the r's:** - Position 3: **r** (count = 1) - Position 8: **r** (count = 2) - Position 9: **r** (count = 3) 3. **Check the rest:** s, t, a, w, b, e, and y are not r's. Total: **3**
2.4s200 output tokens

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

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 5.5

The error means `users` is `undefined` when `UserList` renders, so `.map` is called on nothing. The component destructures the `users` prop, but the parent didn't pass it, or passed `undefined`. ## Common causes **1. The parent doesn't pass the prop, or uses a different name** ```jsx <UserList /> // users is undefined <UserList user={users} /> // wrong name: "user" instead of "users" ``` **2. The data hasn't loaded yet (most common with fetched data)** ```jsx function App() { const [users, setUsers] = useState(); // undefined initially useEffect(() => { fetch('/api/users').then(r => r.json()).then(setUsers); }, []); return <UserList users={users} />;…
5.1s888 output tokens

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

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 5.5

## Issues **Correctness and robustness** 1. **Bare `except:`** catches everything, including `KeyboardInterrupt` and `SystemExit`, so Ctrl+C may not stop the program. Catch specific exceptions: `requests.RequestException` for network problems and `ValueError` for invalid JSON. 2. **Retries non-retryable errors.** A 404 or 401 won't succeed on retry, so retrying wastes time. Only retry transient failures such as 429, 5xx, timeouts, and connection errors. 3. **Sleeps after the final attempt.** The loop sleeps even when no retry follows. 4. **Fixed sleep with no backoff.** Exponential backoff is the standard approach for retries. 5. **Silent failure.** Every failure returns `[]` with no loggin…
18.1s4096 output tokens

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

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Frequently asked questions

Which is cheaper, Claude Haiku 5.5 or GPT-6 Luna?
Both are $0.5275 per 1M output tokens on FastMetal (US dollars, before tax).
How do the context windows of Claude Haiku 5.5 and GPT-6 Luna compare?
Claude Haiku 5.5 takes 1,000,000 tokens; GPT-6 Luna takes 1,050,000.
Can I use Claude Haiku 5.5 and GPT-6 Luna with the same API key?
Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "anthropic-claude-haiku-5-5" or "gpt-6-luna" 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 5.5 and GPT-6 Luna from the browser chat and the API. No monthly fee.

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