OpenAI is offering unlimited text conversations with "Luna," a lightweight version of its latest GPT-5.6 model, to ChatGPT free users and subscribers of the low-cost "Go" plan starting this week, according to the IT industry on August 10. Usage limits remain on image generation, voice conversations, and file attachments. GPT-5.6 consists of three sub-models: Sol, Terra, and Luna, with Luna having the lowest performance but fastest speed, rated on par with Google's Gemini 3.6 Flash in the AI intelligence index by Artificial Analysis. This contrasts with competitors like Google and Anthropic, which have restricted free users' access to latest models. For business-to-business services, OpenAI lowered developer API usage fees by 20–80% at the end of last month. These moves are interpreted as a strategy to increase advertising impressions, as OpenAI began trial operations of its ChatGPT advertising program in the United States earlier this year and expanded it to South Korea in June. The strategy aims to solidify ChatGPT's dominance among individual users, who still make up a high proportion of OpenAI's user base, though its market share has weakened from an overwhelming 80–90%. According to First Page Sage, as of last month, global AI chatbot market shares were 51.3% for ChatGPT, 27.7% for Gemini, and 10.3% for Claude.