GPT 5.6 Luna is the cost-efficient entry in OpenAI's GPT 5.6 family, which also includes the Terra balanced tier and the Sol flagship. OpenAI framed Luna as a strong-capability, affordable option aimed at high-volume, latency-sensitive workloads, positioned for chat, classification, and lightweight agentic workflows where throughput and price matter more than peak intelligence. The model runs through providers on OpenRouter's routing layer, and a price reduction reported at the end of July 2026 cut the underlying OpenAI list price to roughly $0.20 per million input tokens and $1.20 per million output tokens, reinforcing its role as the cheapest tier in the family.
Because Luna shares its lineage with the rest of the GPT 5.6 generation, it benefits from the family's emphasis on getting more useful work from every token and on coordinating multiple agents under an ultra mode for demanding tasks, even though Luna itself is tuned for efficiency rather than the top tier's coordinated-agent setting. It supports multimodal input including text, images, and PDFs while producing text output, and it is offered with reasoning, tool calling, structured output, and temperature controls. Practical fit centers on everyday automation and content pipelines where the GPT 5.6 series demonstrated competitive efficiency on long-running professional evaluations, while frontier-grade coding, science, and cybersecurity workloads remain better served by moving up to Terra or Sol.
