OpenAI is upgrading Free and Go ChatGPT users to GPT-5.6 Luna, replacing GPT-5.5 Instant. These users will now receive unlimited text chats, removing previous text-based rate limits. While file uploads, images, and other tools will still have limits, a new 'Think' button will be introduced, enabling higher reasoning capabilities.

For ChatGPT Plus and Pro subscribers, the GPT-5.6 Sol model is now available, offering enhanced fact reliability and more focused responses. A new slider allows users to control the depth of thought ChatGPT applies to its answers, and the model has been optimized to avoid unnecessary details or formatting, providing more precise information.

OpenAI states GPT-5.6 Sol aims to reduce errors, particularly concerning dates, numbers, and rules. This 'Sol' update is exclusive to ChatGPT's chat function, leaving the Work and Codex versions unchanged. The changes, including the GPT-5.6 Sol model and slider for paid users, are effective immediately. GPT-5.6 Luna will roll out to Free and Go users this week, with unlimited text chats and the Think button arriving next week.