TheModelDesk

On September 22, 2026, OpenAI announced GPT-6 Sol and GPT-6 Luna, extending the GPT-6 family after GPT-6 Astra appeared earlier in September. OpenAI had described Astra as its most capable model and as the world’s best model for several activities, including computer work and coding. The company says Sol and Luna bring Astra’s capabilities to more efficient and accessible models.

The first Sol and Luna models arrived earlier in 2026 as different tiers in OpenAI’s model lineup. Sol is aimed at complex work such as coding. Luna targets high-volume clerical tasks with clear goals, including document summaries, information extraction, and quick answers.

OpenAI says API access to the GPT-6 versions costs half as much as the 5.6 series. The company attributes the reduction to improvements in caching and inference. It also reports better factual accuracy and fewer coding errors.

OpenAI’s internal factuality evaluation used de-identified real-world conversations in which users had flagged model mistakes. The company says GPT-6 Sol makes about half as many mistakes as its predecessor and reaches Astra-level reliability at a lower cost.

OpenAI also claims that Sol and Luna outperform Anthropic’s leading models, including Fable and Opus. Anthropic released Opus 5.5 about 90 minutes before OpenAI announced the new models.

GPT-6 Sol and Luna are available in ChatGPT Work and Codex for most paid accounts, and through the ChatGPT API. Luna is also available in the desktop app and for Free and Go users. OpenAI plans to add the models to the ChatGPT app and website gradually during the day.