Prompt Caching Patterns

Anthropic's prompt caching cuts input-token cost by ~90% on cached prefixes and reduces latency. Worth learning because one mistake (putting a dynamic value before a stable prefix) disables the whole cache.

Cache Mechanics

• TTL: default 5 minutes; ttl: "1h" for 1-hour cache (higher base cost but longer-lived).
• Minimum size: 1024 tokens per cache block for Sonnet/Opus, 2048 for Haiku.
• Max breakpoints: 4 per request.
• Order matters: everything BEFORE a cache_control block is part of that cache key. Dynamic content AFTER the cached block doesn't break the cache.

Anatomy of a Cached Request

from anthropic import Anthropic