GPT-6 Sol vs Luna: What's the Difference, and Which Should You Use?

In this guide

1. The one-sentence version
2. What's actually better?
3. Who should use Sol?
4. Who should use Luna?
5. How do they compare with Claude and Gemini?
6. The verdict

On September 22, 2026, OpenAI released two new models: GPT-6 Sol and GPT-6 Luna. They sit below OpenAI's top model, GPT-6 Astra, and bring many of its improvements to much cheaper tiers.

Here's what each one is and which you should care about.

The one-sentence version

Sol is the smart everyday workhorse. Luna is the fast, very cheap option for doing lots of simple things at scale.

Both prices are half of GPT-5.6's promotional rates for the matching tiers.

What's actually better?

OpenAI says the new models were trained with methods similar to GPT-6 Astra's, with gains in professional work, factuality, coding, computer use and alignment. The headline claim is that GPT-6 Sol makes about half as many mistakes as GPT-5.6 Sol.

That's OpenAI's own measurement, so treat it as a claim rather than a verdict. Independent testing is still coming in, and we'll update our standings as it does.

Who should use Sol?

• ChatGPT users doing real work: writing, analysis, planning and research.
• Developers using Codex or GitHub Copilot. Sol showed up in GitHub's model picker on launch day.
• Businesses that want near-frontier quality without paying premium-tier prices of $10/$50.

OpenAIGPT-6 SolLanguage model · $2 in / $10 out

Who should use Luna?

• App builders running chatbots, support agents or content moderation at scale.
• Data jobs like tagging, sorting, extracting and summarising thousands of documents.
• Anyone for whom speed matters more than depth.

At $0.10 per million input tokens, you could process roughly 750,000 words of input for about ten cents. Try the numbers yourself in our AI cost calculator.

How do they compare with Claude and Gemini?

This week Claude Opus 5.5 took our #1 spot, and it costs $4/$20, twice Sol's price. Gemini 3.8 Flash is Luna's closest rival on value, at $0.75/$3.75 until the end of 2026. See them side by side:

• GPT-6 Sol vs Claude Opus 5.5
• GPT-6 Luna vs Gemini 3.8 Flash
• GPT-6 Sol vs GPT-6 Luna

The verdict

For most people using ChatGPT, Sol is the upgrade you'll notice. For builders, Luna is the one that changes the maths on what's affordable to automate.

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