OpenAI cuts GPT-5.6 Luna price by 80%, adds Fast mode for Sol

GPT-5.6 Luna now costs $0.20 per million input tokens and $1.20 per million output (down 80%); Terra drops 20% to $2/$12. GPT-5.6 Sol gains Fast mode in the API — up to 2.5x speed at 2x price with no change in intelligence.