OpenAI Expands GPT‑6 Lineup with Lower‑Cost Sol and Luna Models

More Affordable and Accurate AI for Coding and Office Work

Earlier this month OpenAI unveiled GPT‑6 Astra, touting it as its most powerful model and “the world’s best model” for tasks ranging from computer work to coding. Now the company is extending the GPT‑6 family with refreshed versions of its smaller Sol and Luna models.

“GPT‑6 Astra introduced a new generation of intelligence; these models extend its benefits by making that intelligence more efficient and accessible,” OpenAI wrote in its announcement.

Sol and Luna debuted earlier this year, each targeting a distinct tier of OpenAI’s hierarchy. Sol is built for complex duties such as coding, while Luna is positioned for high‑volume clerical tasks like summarizing documents, extracting information, or answering quick questions.

OpenAI is highlighting substantial efficiency gains and a price reduction for API access. The new Sol and Luna cost half as much as the previous 5.6 series, a saving the company attributes to better caching and inference processes.

The models also claim higher factual accuracy. In an internal evaluation based on de‑identified real‑world conversations where users flagged errors, GPT‑6 Sol makes about half as many mistakes as its predecessor, achieving Astra‑level reliability at a lower price.

“On our internal factuality evaluation, which is based on de-identified real-world conversations where users flagged mistakes by our models, GPT-6 Sol makes about half as many mistakes as its predecessor, reaching Astra-level reliability at much lower cost,” the announcement reads.

OpenAI asserts that the new Sol and Luna outperform rival Anthropic’s top offerings, including Fable and Opus. Anthropic released a new version of Opus 5.5 just 90 minutes before OpenAI’s launch, underscoring the fierce competition between the two firms.

The updated Sol and Luna are now available in ChatGPT Work and Codex for most paid accounts, as well as through the ChatGPT API. Luna will also appear in the desktop app and for Free and Go users. OpenAI plans to roll the models out to the ChatGPT app and website throughout the day.