In two days three labs released new models, and all three talk about price first.
OpenAI comes in with its two smaller models and the simplest argument on the market: half price. Astra stays on top for the heaviest work, and Sol and Luna are for everything else that runs all day.
Fact
The facts: on 22 September 2026 OpenAI introduced GPT-6 Sol and GPT-6 Luna, trained with methods similar to GPT-6 Astra, which the company released earlier in the month. API prices are 50% lower than GPT-5.6's promotional pricing: Sol costs $2 per million input tokens and $10 per million output tokens (from $4 and $20), and Luna $0.10 and $0.50 (from $0.20 and $1.20). Per OpenAI, on AutomationBench Sol at xhigh effort outperforms Claude Opus 5 at max effort at 9% of the cost per task, and on their internal factuality test, built on conversations in which users flagged an error, Sol makes about half as many mistakes as its predecessor. Cached input reads get a 90% discount. The models are available in ChatGPT Work and Codex for Plus, Pro, Business, Enterprise and Edu users, Free and Go users get Luna in the desktop app, and in the API they are gpt-6-sol and gpt-6-luna. The publication date was checked against OpenAI's feed and the Vercel and Microsoft announcements from the same day; the page's hidden tag shows 29 September, when a note about GPT-6.1 Sol was added.
The mistakes
The benchmark points are OpenAI's, measured at different effort levels, while the other models' numbers are taken from public reports.
The number that matters is the mistakes. The test is built precisely on conversations where people caught the model in an error, which makes it harder than typical use. Half the mistakes there means a lookup you will correct less often. It does not mean a lookup you can skip checking.
Cheaper is nice. Fewer mistakes are worth more.
With Luna the output price falls more than the input price, from $1.20 to $0.50, and in a product with long answers the difference shows in the first month.
Official primary sources
OpenAI - Introducing GPT-6 Sol and Luna, 22.09.2026Vercel Changelog - GPT-6 Sol and Luna now available on AI Gateway, 22.09.2026Microsoft Azure Blog - GPT-6 Astra, Sol, and Luna for production agents in Microsoft Foundry, 22.09.2026The visual is generated code-art, no third-party images.