OpenAI has expanded the GPT-6 generation with updated versions of its smaller Sol and Luna models, following the launch of GPT-6 Astra earlier this month. Astra was heralded by OpenAI as its most powerful and capable model yet and the “world’s best model” for a range of activities, including computer work and coding. The first Sol and Luna models were introduced earlier this year as different tiers in OpenAI’s model hierarchy, and the company says the updated versions extend Astra’s benefits by making that intelligence more efficient and accessible.

OpenAI describes Sol as designed for complex tasks like coding, while Luna is aimed at high-volume clerical work with a clear goal, such as summarizing documents, extracting information, or answering quick questions. The release emphasizes efficiency and affordability, most notably through a substantial API price cut: the 6 series models will be available at half the cost of the 5.6 series Sol and Luna. OpenAI attributes the reduction to improvements in caching and inference. The company also claims improved factual accuracy and a lower error rate on coding tasks. On its internal factuality evaluation, which is based on de-identified real-world conversations where users flagged mistakes, OpenAI says GPT-6 Sol makes about half as many mistakes as its predecessor, reaching Astra-level reliability at much lower cost.

As with previous releases, OpenAI directly compares the new models with Anthropic’s top models, claiming that GPT-6 Sol and Luna handle tasks substantially better than Anthropic’s Fable and Opus models. The competitive tension was visible in timing: Anthropic released a new version of Opus 5.5 just 90 minutes before OpenAI’s announcement.

The updated Sol and Luna models are now available in ChatGPT Work and Codex for most paid accounts and in the ChatGPT API. Luna is also available in the desktop app and for Free and Go users. OpenAI expects to roll out the models to the ChatGPT app and website gradually throughout the day.