How prompt caching works
When you send a request with prompt caching enabled:
- The system checks if a prompt prefix, up to a specified cache breakpoint, is already cached from a recent query.
- If found, it uses the cached version, reducing processing time and costs.
- Otherwise, it processes the full prompt and caches the prefix once the response begins.
This is especially useful for:
- Prompts with many examples
- Large amounts of context or background information
- Repetitive tasks with consistent instructions
- Long multi-turn conversations
By default, the cache has a 5-minute lifetime. The cache is refreshed for no additional cost each time the cached content is used.
The lifetime is measured from the start of the request that writes or reads the cache entry, not from the end of its response. Time spent generating a response counts against the lifetime: if a response takes 4 minutes to stream, a follow-up request that reuses the same cached prefix must start within about 1 minute of that response completing.
If you find that 5 minutes is too short, Anthropic also offers a 1-hour cache duration at additional cost.
For more information, see 1-hour cache duration.
Prompt caching caches the full prefix
Prompt caching references the entire prompt - tools, system, and messages (in that order) up to and including the block designated with cache_control.