GPT-6 Sol and Luna bring OpenAI's new generation to half the API price of GPT-5.6

On September 22nd, OpenAI released two new models, GPT-6 Sol and GPT-6 Luna. They're the smaller members of the GPT-6 family, which started with GPT-6 Astra at the beginning of the month. OpenAI trained them with similar methods to Astra, and priced them for everyday work at scale.

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openai.com · Introducing GPT-6 Sol and Luna · Sep 22, 2026

OpenAI releases GPT-6 Sol and GPT-6 Luna

September 22, 2026 API, ChatGPT and Codex

Here's how the family fits together, priced per million tokens. Astra is still OpenAI's most capable model, for the hardest work, at ten dollars in and fifty out. Sol is the balance of capability and cost, at two dollars in and ten out. And Luna is for focused, high volume tasks, at ten cents in and fifty cents out. All three read text and images, and take up to about a million tokens of context.

The headline for anyone paying for the API is price. Sol and Luna cost half what their GPT-5.6 versions did at those models' promotional prices. OpenAI puts that down to better caching and cheaper serving. Repeated context is billed at a tenth of the normal input price, and OpenAI says caching now hits more often by default on GPT-6, which matters most for agents that resend long conversations.

Next, what OpenAI says they can do.

These are OpenAI's own evaluations, and the competitor scores come from other companies' published reports, so treat them as OpenAI's claims. On a test of business workflows across apps, Sol on its extra high setting beat Claude Opus 5 on its maximum setting, at under a tenth of the cost per task. On a test of long software engineering tasks, it came within about a point of the best score from Claude Fable 5, for roughly eighty percent less per task. And Luna, the cheap one, was comparable to Claude Opus 5 at medium effort on that coding test, for ninety three percent less.

Two changes you'd notice in conversation. On conversations where people had flagged a factual error from an earlier model, Sol made about half as many mistakes as GPT-5.6 Sol. OpenAI says those conversations are harder than typical use. And both models pick up the way Astra talks: clearer, with less jargon, fewer details you didn't need, and slightly shorter answers.

Finally, who can use them.

If you pay for ChatGPT, on Plus, Pro, Business, Enterprise or Edu, both models are in ChatGPT Work and in Codex. They aren't in regular ChatGPT chat yet. On the Free or Go plans, you can try Luna in the desktop app. And developers can call both through the API now.

One thing to know if you tried them in the first few days. On September 25th, OpenAI fixed a bug in how images were encoded, which had weakened image understanding in Sol and Luna, in the API and in Codex, including computer use. If your work involves images, OpenAI recommends running your evaluations again.

OpenAI is clear that Astra is still its best model, and the one to use when results matter most. The announcement and the API changelog have the full numbers. That's GPT-6 Sol and Luna: OpenAI's new generation, at half the API price of GPT-5.6.