OpenAI announces an improved version of GPT-5.6 Sol in ChatGPT with better accuracy and consistency, and expands access to GPT-5.6 Luna for free users, including unlimited everyday chats.
From the source
ChatGPT introduces improved GPT-5.6 Sol with better accuracy and consistency, plus expanded access for free users and unlimited everyday chats with GPT-5.6 Luna.
openai.com