Anthropic Silently Dropped Prompt Cache TTL from 1 Hour to 5 Minutes

This is a follow-up to my earlier article on Claude prompt caching, which has become one of my most-read pieces. Since publishing it, I've been tracking a regression that Anthropic has not publicly announced. On March 6, 2026, Anthropic changed the default prompt cache TTL from 1 hour to 5 minutes. If you're running Claude API calls with prompt caching and you haven't touched your code recently, your cache hit rate is likely near zero right now. What Changed Previously, when you sent a request with cache_control: {"type": "ephemeral"}, the cached prompt would persist for 1 hour by default.