OpenAI launches GPT-6 Sol and Luna with lower prices and Astra-level upgrades

OpenAI has launched GPT-6 Sol and GPT-6 Luna, two new models that bring some of the improvements introduced with its flagship GPT-6 Astra to faster and significantly cheaper options for everyday work.

The company introduced Astra earlier this month and describes it as its most capable model, reserved for the most demanding workloads. Sol and Luna were trained using similar methods, but are designed around different levels of cost and performance. Sol targets complex coding, agentic and professional tasks, while the smaller Luna is intended for high-volume workloads where lower cost matters more. Astra remains at the top of the GPT-6 lineup.

One of the biggest changes is price. OpenAI has cut API pricing for both models by 50% compared with their GPT-5.6 predecessors. GPT-6 Sol costs $2 per million input tokens and $10 per million output tokens, while Luna costs $0.10 and $0.50, respectively. OpenAI attributes the lower prices to improvements in caching and inference.

OpenAI's benchmarks suggest Sol can approach the performance of more expensive frontier models at a substantially lower cost. On DeepSWE v1.1, which tests agents on complex software engineering tasks in real codebases, GPT-6 Sol scored 68.8%, within 1.1 percentage points of Claude Fable 5's 69.9%, while costing approximately 80% less per task. GPT-6 Luna scored 66.6% on the same benchmark.

The company also claims a significant improvement in factual accuracy. In an internal evaluation based on conversations where users had previously flagged factual errors, GPT-6 Sol made about half as many mistakes as its predecessor. OpenAI has also improved prompt caching across the GPT-6 family, offering discounts of up to 90% on cached input-token reads. GitHub says caching improvements have reduced the share of prompt tokens requiring fresh processing by more than half across billions of requests over the past several months.

GPT-6 Sol and Luna are available in ChatGPT Work and Codex for Plus, Pro, Business, Enterprise and Edu users. Free and Go users can access Luna through the desktop app. The models are also available through the API as gpt-6-sol and gpt-6-luna. They are not yet available in regular ChatGPT conversations, with OpenAI rolling out access gradually throughout the day.