OpenAI updates GPT-5.6 Sol in ChatGPT and opens unlimited free chats on Luna

OpenAI announced an update to GPT-5.6 Sol in ChatGPT for Plus and Pro subscribers, alongside expanded access to the lighter GPT-5.6 Luna model for free users. By the company's own internal evaluations, the updated Sol makes 68% fewer factual errors compared to GPT-5.5 Instant, while Luna cuts errors by 62% on financial, medical and legal prompts. ChatGPT now has more than 1 billion weekly users.

For paid subscribers, the separate Instant and Thinking modes are being replaced with a single thinking slider that lets users choose how much reasoning the model applies to a given answer. The updated Sol is tuned for everyday tasks — quick questions, web search, planning, research, advice, writing and more complex decisions — while aiming for more direct answers without padding them with unnecessary detail. For free users, GPT-5.6 Luna becomes the default model this week, with unlimited text chats (subject to abuse guardrails) and a new Think button arriving next week to give Luna more time to reason through harder questions — limits on file uploads, images, voice chats and image generation stay in place.

• GPT-5.6 Sol (Plus/Pro): 68% fewer factual errors than GPT-5.5 Instant
• GPT-5.6 Luna (free): 62% fewer errors on financial, medical and legal prompts
• Unlimited text chats for free users arrive next week

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