OpenAI Upgrades ChatGPT to GPT-5.6 Luna and Sol
OpenAI has upgraded the default model for free ChatGPT users to GPT-5.6 Luna, while updating Plus and Pro users to an optimized GPT-5.6 Sol model. Paid users also receive a new slider to adjust the model's thinking depth, and free users will get unlimited text chats and a "Think" button starting next week. This update democratizes advanced reasoning capabilities by bringing GPT-5.6 Luna to free users, while giving paid subscribers granular control over latency and reasoning depth. It marks a significant step in making high-level AI reasoning more accessible and customizable for everyday tasks. The updated GPT-5.6 Sol for paid tiers is specifically optimized for everyday conversations and is restricted to the standard chat interface, leaving the versions powering Work and Codex unchanged. Free users will still face limits on file uploads, image generation, and other advanced tools.
## BACKGROUND
Released in July 2026, GPT-5.6 is OpenAI's large language model family consisting of three variants: Luna (economic/lightweight), Terra (mid-tier), and Sol (most capable). Previously, ChatGPT separated quick responses and deep reasoning into different modes, but this update unifies them under a single model with adjustable thinking time.