OpenAI announced that this week, the default model for all ChatGPT users will be switched to GPT-5.6 Luna. This model reduces factual error rates by 62% compared to the previously default GPT-5.5 Instant. Free users and Go plan subscribers will gain unlimited text conversation access and a new "Think" button to trigger a higher intensity reasoning mode. Meanwhile, Plus and Pro paid users will receive the optimized GPT-5.6 Sol model and a new "slider" tool to adjust the model's depth of thought. This round of upgrades comes after OpenAI already lowered the prices of its GPT-5.6 Luna and Terra models last week, reflecting an accelerating trend of price reductions amid intensifying competition in the AI industry.