GPT-5.6 Luna is OpenAI's cheapest current model, and after an 80% price cut three weeks into its life it became one of the most-used models on the open market. ........ Luna launched July 9, 2026 at $1 per million input tokens and $6 output; on July 30 OpenAI cut that by 80% to $0.20 and $1.20. On August 6, 2026, OpenAI announced Luna would become the default model for ChatGPT Free and Go accounts, with unlimited text chats. It shares the GPT-5.6 family's roughly 1.05 million