OpenAI GPT-5.6 Luna targets cost-sensitive, high-volume workloads — the cheapest and fastest tier of the GPT-5.6 family, while keeping the same 1,050,000-token context window and 128,000-token max output. Supports text and image input, web search, and reasoning effort / summary display options. Ideal for chatbots, classification, routing, batch summarization, and other tight-loop tools where per-call cost matters most; upgrade to Terra or Sol when a task needs more capability.