A new default for free users
On August 6, OpenAI announced an updated GPT‑5.6 Sol for ChatGPT Plus and Pro and said GPT‑5.6 Luna would become the default for Free and Go users this week. Luna targets quick everyday conversations, while Sol is positioned for longer reasoning and complex work. Unlimited text chats and a Think button that requests more reasoning are scheduled for Free and Go next week.
“Unlimited” applies to text conversations, not every feature. Existing limits remain for file uploads, image generation and other tools, and abuse safeguards still apply. The Sol update concerns the ChatGPT conversation experience; OpenAI says the versions used in Work and Codex are unchanged.
Vendor-reported evaluation
OpenAI reports that, on its internal factuality evaluation, answers containing factual errors fell by about 62% for Luna and 68% for Sol relative to GPT‑5.5 Instant. These are vendor-selected internal results, not an independent benchmark. Error rates can change by language, topic, browsing behavior and real-world question mix, so consequential answers still require primary-source checks.
What users should verify
Rollout timing can vary by account, so users should check the model label and Think control in their own app. Unlimited text does not mean unlimited access to advanced tools. Medical, legal and financial decisions still need qualified human review and source verification.