The new GPT-5.6 family: Luna, Terra, Sol

OpenAI released three new language models called GPT-5.6 (Luna, Terra, and Sol, in order of size) that are available to the public as of July 9th, 2026. These models have a one-million token context window (the amount of text they can consider at once) and perform particularly well on long-running agent tasks (workflows where an AI works independently over many steps), outperforming competitors like Claude Fable 5 at lower cost. OpenAI also added new API features including programmatic tool calling (letting the model write and execute code to coordinate different tools), multi-agent support (spawning smaller AI instances to work in parallel), and prompt cache breakpoints (explicit markers for caching repeated input text).