OpenAI has updated GPT-5.6 Sol in ChatGPT for Plus and Pro subscribers, shipping a version that the company says cuts unnecessary detail and excess formatting. At the same time, free-tier users are being shifted to GPT-5.6 Luna, the smallest and cheapest model in the GPT-5.6 family, with unlimited text chats set to arrive next week.
What changed in Sol
The Sol update brings two changes for paying users. The model now produces shorter, more direct answers for simple queries while preserving depth for complex tasks. OpenAI also claims a reduction in factual errors. In an internal evaluation using prompts from finance, medicine, and law, responses containing at least one factual mistake dropped by roughly 62 percent for Luna and 68 percent for Sol compared with GPT-5.5 Instant. These figures have not been independently verified.
A new reasoning-effort slider lets paying users choose from five levels of processing depth. Lower settings handle everyday questions, while higher settings are intended for research, planning, and coding. The slider was previously available only in ChatGPT Work. OpenAI positions it as a way to make quick answers and deep reasoning feel like one model rather than two separate experiences.
The free tier tradeoff
GPT-5.6 Luna becomes the default model for Free and Go users later this week. Unlimited text chats follow next week, along with a Think button that lets Luna reason longer on harder questions. But Luna does not switch to a stronger model when it struggles. Smaller models are generally more error-prone than larger reasoning counterparts, and the Think button extends Luna's processing time without upgrading the underlying model. Free users lose access to OpenAI's most capable reasoning altogether.
The Sol changes apply only to ChatGPT. The model remains unchanged in ChatGPT Work and Codex. Limits on file uploads, image generation, and other tools stay in place for free users.
The update is the latest step in a tiered strategy that has defined OpenAI's 2026 product releases. The company cut GPT-5.6 Luna API pricing by 80 percent shortly after launch and has since used Luna as the entry point for free users while reserving Sol for paying subscribers. Whether a reasoning slider meaningfully improves the experience remains an open question. OpenAI's own model switcher, introduced with GPT-5, was largely ignored by users.
