On June 26, 2026, OpenAI officially previewed GPT 5.6, a model family of three tiers: Sol, Terra, and Luna. The launch was one of the most discussed AI events of the year due to measurable capability gains and an unprecedented U.S. government-gated rollout that limited initial access to approximately 20 trusted partner organizations. GPT 5.6 is the successor to GPT 5.5, which launched on April 23, 2026, making this a sub-60-day iteration cycle. The three-tier architecture uses a new naming convention: Sol is the flagship model for the hardest tasks including complex multi-step coding, cybersecurity research, agentic workflows, and quantitative biology analysis, introducing "max" and "ultra" reasoning effort modes. Terra is the balanced model for everyday work, delivering competitive performance to GPT 5.5 at approximately 2x lower cost, designed for high-volume business tasks.