GPT-5.6 Luna is the cost-efficient member of OpenAI's GPT-5.6 family, which reached general availability alongside the Sol flagship and Terra balanced model. OpenAI's launch materials describe Luna as the tier designed to deliver capable behavior at the lowest cost in the lineup, and an update on July 30, 2026 cut its price by 80% to sharpen that positioning. Within that family, Luna is built to handle the everyday workload of broad consumer use, sitting below Sol's deeper reasoning tier while still inheriting the family's training emphasis on getting more useful work from every token.

In practice, Luna's role is best understood through its ChatGPT deployment. On August 6, 2026, OpenAI made Luna the default model for Free users, expanding access with unlimited text chats while preserving a path to harder questions through a new Think button that adds higher reasoning on demand. That placement signals a model intended for fast, high-volume conversational use, where reliability on common questions matters more than pushing the absolute frontier of capability. It also marks a notable expansion in who can reach a GPT-5.6 family model, broadening the audience for Luna beyond paid subscribers.