Review of Anthropic Prompt Caching
Prompt caching is a feature of the Claude API that lets you cache large context (system prompts, documents, code) for 5 minutes at a time. Subsequent calls within the cache window get a 90% discount on cached tokens and much faster response times. Launched in August 2024, it's one of the most useful Claude API features for production apps.
90% cost reduction on cached tokens. Cached input tokens cost 10% of regular input tokens. For a 50K token system prompt, this is a massive saving.
5x faster first-token latency. Cached content is served from the cache, not re-processed. First-token latency drops from 5-10 seconds to under 1 second for long contexts.
5-minute cache window is practical. Long enough for chat sessions, code reviews, and multi-turn tool use. Short enough that storage costs are manageable.
No code changes for many use cases. Add cache_control breakpoints to your messages array. The API handles the rest.
Works with all Claude models. Sonnet, Opus, and Haiku all support prompt caching. Same discount applies.
5-minute window only. For batch processing or long-running sessions, the cache can expire mid-task. Anthropic is working on longer windows.
Cache invalidation is manual. You need to set cache_control breakpoints correctly. Get them wrong and you won't get the cache hits.
No persistent cache. Each cache is per-API-key and ephemeral. If you restart your server, the cache is gone.
Costs add up for high-frequency apps. The 5-minute window can be too long for low-traffic apps where the cache isn't reused enough.
Cache write: 25% premium on input tokens (one-time, when first cached). Cache read: 10% of input token cost. Cached tokens also get faster processing. For 50K context apps, the savings are massive.
Any Claude API user with long system prompts, large documents, or multi-turn conversations. RAG apps, code review tools, customer support agents — all benefit.
★ 5/5. The single biggest cost optimization for Claude API. If you're not using it, you're overpaying. Implement it today.
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