OpenAI's new prompt caching adds explicit breakpoints and a miss-diagnostics tool.

The GPT-6 caching update lets you mark cache breakpoints, change reasoning effort mid-conversation without invalidating the cache, and prewarm before a user request arrives. Cached input discounted up to 90%, shared prefixes eligible for 30 minutes, and a dashboard that names the cause of each miss. Compare that to Anthropic's current situation, where changing top-level effort between requests silently invalidates your cache unless you use the per-message beta.