GPT-5.6 Sol Gets a Big Accuracy Upgrade, GPT-5.6 Luna Opens Up to Free Users

OpenAI has shipped an updated version of GPT-5.6 Sol in ChatGPT focused on accuracy and consistency, and separately is expanding access to GPT-5.6 Luna for free users — making it the default model for the Free and Go tiers this week.

Details

• Fewer factual errors: The updated Sol reduces factual errors by roughly 68% compared with GPT-5.5 Instant in financial, medical, and legal contexts where precise details matter, according to OpenAI
• Tighter, more useful responses: Sol is tuned to give more direct answers, use tighter formatting, and skip extra detail when it doesn’t help — while making better use of retrieved sources for answers that depend on dates, numbers, sources, rules, or assumptions
• More consistent across modes: OpenAI says behavior is now more consistent between Sol’s instant and deeper-reasoning modes, reducing cases where the two modes gave noticeably different answers
• Reasoning-depth slider for paid users: Plus and Pro subscribers get a new slider to control how much reasoning depth Sol applies, available on web, mobile, and desktop
• Luna becomes the free default: GPT-5.6 Luna becomes the default model for Free and Go users this week, with unlimited text chats following next week
• New Think button coming: A new “Think” button for tackling complex questions launches next week for free users, though it will be subject to abuse-prevention safeguards
• Some limits remain: Rate limits still apply to file uploads, image generation, and other tools even after unlimited text chat rolls out
• Scope of the change: The chat-optimized version of Sol described here is limited to ChatGPT’s Chat experience; the Work and Codex versions of Sol are unchanged

What happened next

The update effectively narrows the gap between what free-tier and paid users get in ChatGPT’s default chat experience, at least for text conversations — while keeping paid-only controls like the reasoning-depth slider as a differentiator. OpenAI did not specify exact dates for the “next week” rollouts of unlimited chats and the Think button, so free users should expect the features to arrive on a rolling basis rather than all at once.