OpenAI made GPT-5.6 Luna ChatGPT’s default model, giving free users unlimited text chat and a Think button.

OpenAI said it would switch ChatGPT’s default model for all users to GPT-5.6 Luna during the week. Compared with the previous default, GPT-5.5 Instant, Luna reportedly produced responses containing at least one factual error 62% less often.

Free and Go-plan users receive unlimited text chat. They also gain a new Think button that lets them select a higher level of reasoning for more complex questions.

Plus and Pro users receive an updated GPT-5.6 Sol model designed to improve factual reliability and provide more focused answers. OpenAI said Sol uses more compact formatting, removes unnecessary detail and maintains a more consistent tone across everyday conversation, research, advice, planning, writing and decision tasks.

Plus and Pro accounts also receive a slider controlling how much reasoning the model applies to an answer. OpenAI said the updated Sol model and slider became available to those subscribers on Aug. 6.