GPT-5.6 pricing updates and Fast mode launch

Starting July 30, GPT-5.6 Luna costs 80% less, while GPT-5.6 Terra costs 20% less. See pricing details.

Introduced Fast mode in the API, which replaces Priority Processing. For GPT-5.6 Sol, Fast mode delivers up to 2.5× faster speeds than standard processing at twice the price. This change is backward compatible: requests tagged priority will automatically use Fast mode.