On June 27, OpenAI announced the launch of a limited preview for its GPT-5.6 model series. This series includes three models: the flagship model Sol, the balanced model Terra for daily work, and the fast and economical model Luna. Among them, Terra offers performance comparable to GPT-5.5 but at half the cost; Luna provides powerful capabilities at an extremely low cost. The GPT-5.6 Sol is equipped with OpenAI's most robust safety protection system to date, enhancing defenses against high-risk activities, sensitive web requests, and repetitive abusive behaviors. OpenAI also dedicated several weeks to conducting system vulnerability searches and stress testing to improve its ability to withstand real-world attacks. The company plans to fully release these three models in the coming weeks. As part of its ongoing communication with the U.S. government, OpenAI provided an advanced preview of its release plans and model capabilities to the government before the official Friday announcement. Notably, the GPT-5.6 Sol is OpenAI's most powerful model to date.