GPT-6 Luna

GPT-6 Luna is the budget sibling in OpenAI's GPT-6 family, launched September 22, 2026. Where Sol balances performance and cost, Luna optimizes for fast responses and high volume: $0.10 per million input tokens and $0.50 per million output, down from $0.20/$1.20 on GPT-5.6 Luna. It is the model assigned to ChatGPT Free and Go users, rolling out in the Chat tab from October 8, 2026, with the same Intelligent UI treatment as Sol.

The trade-off is capability: coverage notes both models sit only marginally above their GPT-5.6 predecessors in raw capability, and Luna is explicitly tuned for everyday conversation rather than hard reasoning or long agentic runs. For volume workloads — classification, drafting, summarization at scale — it is OpenAI's cheapest path to a current-generation model.