Anthropic Prompt Caching — Cut AI API Costs 90%

What is Prompt Caching?

Anthropic's prompt caching caches repeated content (system prompts, tool definitions, long documents) for reuse across requests; cache reads cost only 1/10.

TL;DR: Anthropic prompt caching. Cache system prompts / tools / documents. Read cost is 1/10. 5-minute TTL auto-renews. Must-use for production Claude apps. Up to 90% savings.

Cacheable Content

1. System prompts — most common case
2. Tool definitions — big wins with many tools
3. RAG documents — multi-turn Q&A over the same doc
4. Multi-turn conversation prefix — cache early context

Best Practices

• Cache the longest, most stable content first
• Cached content must be a prefix
• Monitor cache_read_input_tokens to confirm hits
• Minimum 1024 tokens

FAQ

Q: Does it affect quality? A: No — the model sees identical input either way.

Q: Does Claude Code use it? A: Yes — CLAUDE.md and tool definitions are cached automatically.