Prompt Caching With the Claude API: A Practical Guide

Prompt caching with Claude from Anthropic can indeed be a highly impactful optimization technique to reduce costs and improve performance. Based on your detailed explanation, here are some key takeaways and considerations:

Key Takeaways

1. Caching Configuration:

   • Use the cache_control field in tools or system prompts to set breakpoints.
   • Configure either 5-minute (ephemeral_5m) or 1-hour (ephemeral_1h) TTLs.

2. Prefix Matching:

   • Ensure that the prefix remains stable across requests for cache hits.
   • Avoid adding timestamps, trailing whitespace, or changing tool order in the system prompt.

3. Cost Savings:

   • Caching reduces input token costs significantly (up to 90%).
   • Output tokens still bill at full rate, so caching is less effective if output tokens dominate your cost structure.

4. Hit Rate Observability:

   • While cache hits are observable and generally reliable in practice, there's no guarantee of a write being readable on the next request.

5. Tool Definitions:

   • Adding or modifying tools invalidates caches for all prompts using those tools.

6. **Manual Eviction

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