OpenAI has announced significant price and performance updates to the GPT-5.6 model family, driven by optimizations across model architecture, inference systems, and agentic harnesses. To improve cost-efficiency for enterprise workloads, the company is reducing prices for GPT-5.6 Luna by 80% and GPT-5.6 Terra by 20%. Specifically, Luna provides high-volume capability at approximately 6 cents per task—outperforming Fable 5 with a 99% lower estimated cost per task—while operating at nearly nine times the speed of previous frontier-class models. In the API, a new "Fast mode" replaces Priority Processing for GPT-5.6 Sol, delivering up to 2.5x faster speeds at twice the price of Standard processing without reducing intelligence. These efficiency gains stem from improved routing, optimized production software, and enhanced context management. Notably, GPT-5.6 Sol has been used to autonomously optimize production kernels, reducing end-to-end serving costs by 20% and increasing token-generation efficiency by over 15% through hundreds of automated experiments. The updated API pricing sets Luna at $0.20 per million input tokens and $1.20 per million output tokens, while Terra is priced at $2 per million input tokens and $12 per million output tokens.