OpenAI upgrades GPT-5.6 Sol in ChatGPT and expands GPT-5.6 Luna to free users with unlimited text chats

OpenAI updated GPT-5.6 Sol for Plus and Pro users in ChatGPT to deliver more focused answers, reduced factual errors (internal evals showed ~68% fewer factual errors versus GPT-5.5 Instant on financial/medical/legal prompts), and added a reasoning-depth slider. Free and Go users were upgraded to GPT-5.6 Luna as the default model, with unlimited text chats and a new Think button for higher-reasoning queries rolling out the following week. The Sol variant powering Work and Codex remained unchanged.