GPT-5.6 Terra is OpenAI's mid-tier model in the GPT-5.6 family, built to handle everyday work at a fraction of the cost of the flagship Sol model. ........ Terra sits between Sol (flagship) and Luna (fastest, cheapest) in OpenAI's three-tier GPT-5.6 lineup. At launch, OpenAI described Terra as matching GPT-5.5 while costing half as much. On July 30, 2026, OpenAI cut Terra's price by 20%, on top of an 80% cut for Luna. Terra supports a context window of roughly 1 million token