GPT-5.6 Luna's Price Cut Twice: How OpenAI Cut Agent Reasoning Cost to $0.2 per Million Tokens

On July 30, 2026, OpenAI announced an 80% cut in the input pricing of GPT-5.6 Luna API to $0.2 per million tokens, a 20% reduction for Terra, and no change for Sol. This move came less than three weeks after the general availability of the three-tier models on July 9, reflecting the intensifying AI inference cost war. This article sorts out the new pricing lists for Sol, Terra and Luna, the changes to Prompt Caching and Codex quotas, as well as selection suggestions for cost-sensitive Agent workloads.