GPT-5.6 Luna (AWS Mantle)

GPT-5.6 Luna belongs to OpenAI's GPT-5.6 generation, a sub-family that also includes the GPT-5.6 Sol and GPT-5.6 Terra variants released together in mid-2026. Rather than being positioned as a developer-focused API flagship, Luna is framed by OpenAI as the everyday entry point of the lineup, replacing the previous default for Free ChatGPT users and shipping with unlimited text access for that tier. Columbia University's chat service lists Luna alongside the rest of the GPT-5.6 series in its current model roster, reinforcing its place within this coordinated release wave and signaling broad institutional adoption of the new generation.

OpenAI's rollout messaging emphasizes that Luna is tuned for the most common ChatGPT use cases—quick answers, casual questions, and conversational help—while keeping a path to deeper reasoning through a new Think button that lets Free users invoke higher-effort responses on harder prompts. The split between Luna and the more fact-focused Sol variant reflects a deliberate tiering strategy: Luna covers the broad, high-volume conversational workload, while Sol is aimed at Plus and Pro subscribers who need tighter factual reliability and adaptive detail. Together, the two models give OpenAI a way to serve different audiences from the same GPT-5.6 foundation, with Luna acting as the accessible, widely available workhorse of the family.