openai.comarticle

Better prompt caching for GPT-6

OpenAI describes the improved prompt caching system for the GPT-6 family. Eligible shared prefixes reused within a 30-minute window get discounts of up to 90% on cached input tokens. It adds a Prompt Caching Dashboard for hit rates and input composition, and a diagnostics tool that reports why a request missed the cache (for example `tools_changed`) with affected token counts. It also adds explicit cache breakpoints and cache prewarming. On GPT-6 models, reasoning effort can be changed mid-conversation through an appended `configuration_update` without breaking the cache. For tool changes, it advises keeping tool definitions stable and using `allowed_tools` or `tool_choice: none` instead of removing them. Instruction changes should be appended as new developer messages. This is practical guidance for cutting cost and latency in long-running agent loops.