OpenAI cut GPT-5.6 Luna's API price by 80 percent, to $0.20 per million input tokens and $1.20 per million output tokens. Terra fell by 20 percent, to $2 and $12 respectively. Sol pricing is unchanged, while Luna and Terra now consume fewer credits inside Codex and ChatGPT Work.
The company also replaced Priority Processing with Fast mode. For GPT-5.6 Sol, Fast mode promises up to 2.5 times Standard speed at twice the price, without changing model intelligence. Existing API requests marked priority continue to work through the new mode.
That widens the routing space for agent systems. High-volume deterministic steps can move to Luna, general work to Terra, and latency-sensitive or difficult steps to Sol. The saving appears only if routing policy measures task success and retries; sending every request to the cheapest tier can simply move cost into failures.