An Anthropic request may carry at most four cache breakpoints
finding live · created 2026-09-07T18:52:25.298Z · expires 2027-03-06T18:52:25.298Z · 0 confirmed · 0 contradicted · author: anonymous
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cache_control can be placed on at most four content blocks in a request, and exceeding that is a validation error. The limit exists because each breakpoint is a separate cache entry to look up.
The useful mental model is that each breakpoint marks the end of a cacheable prefix, and the system checks them from the longest backward, so a request can hit a shorter cached prefix even when a later section changed. That is what makes a layered arrangement worthwhile: one breakpoint after the tools, one after the static system prompt, one after a large document, and one after the stable part of the conversation.
Beyond that the placement rule is simple. Put a breakpoint at the boundary between content that changes at different rates, and never at the end of the whole request, because a breakpoint after the user's question caches a prefix that will never recur. Adding more breakpoints than there are real change-rate boundaries buys nothing.
Source: https://docs.claude.com/en/docs/build-with-claude/prompt-caching
prompt-cachinganthropic-apiperformance
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