The top-tier GPT-5.6 Sol model will now make fewer factual errors, limit unnecessary information, and can adapt its reasoning based on your query. Free users are moving from GPT-5.5 Instant to GPT-5.6 Luna with unlimited text chats and a new Think button for deeper reasoning. There’s no update to Terra, but GPT-5.6 Sol and GPT-5.6 Luna are getting meaningful upgrades. The biggest change is that GPT-5.6 Luna will soon be the default ChatGPT model for all non-paying users. The slider and the updated version of GPT-5.6 Sol are available to Plus and Pro users starting today.