Earlier this month, OpenAI introduced GPT-6 Astra, describing it as its most powerful and capable model to date and the "world's best model" across a range of tasks, including computer work and coding. Now the lab is broadening the GPT-6 generation with refreshed versions of its smaller Sol and Luna models. According to the company, "GPT-6 Astra introduced a new generation of intelligence; these models extend its benefits by making that intelligence more efficient and accessible."

The Sol and Luna lines first appeared earlier this year, occupying different tiers within OpenAI's model hierarchy. Sol targets complex work such as coding, while Luna is positioned as better suited to clerical tasks — "high-volume tasks with a clear goal, like summarizing documents, extracting information, or answering quick questions."

OpenAI is also stressing major gains in efficiency and affordability, most visibly through a significant cut to API pricing. The 6 series models will be offered at half the cost of the 5.6 series of Sol and Luna, a reduction OpenAI credits to improvements in caching and inference. The company further claims its newest models are better at delivering factually accurate answers and have a lower error rate for coding. "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 states.

As is customary with OpenAI's model launches, the company asserts that its latest offerings outperform those of its main rival, Anthropic. It repeatedly claims that GPT-6 Sol and Luna handle tasks substantially better than Anthropic's top models, such as Fable and Opus. Notably, Anthropic released a new version of Opus 5.5 just 90 minutes before OpenAI's release, underscoring the fierce competition between the two firms.

The updated Sol and Luna versions are now available in ChatGPT Work and Codex for most paid accounts, and in the ChatGPT API, while Luna will also be available in the desktop app and for Free and Go users. OpenAI expects to roll the models out to ChatGPT (the app and website) gradually over the course of the day.