Verified70% confidenceFactExact time
Whether prompt caching hits depends on byte-for-byte consistency of the request prefix; if even one character at the beginning differs, the entire cache is invalidated.
4
Sources
70%
Confidence
Long-term
Relevance
10/13/2026
First Seen
Sources
Related Entities
Related Claims
UnverifiedIf most of the prompt is repeated and fixed while cache_read_input_tokens stays near zero for a long time, it can be almost certain that the prefix changed between requests.79% similarUnverifiedPlacing a timestamp accurate to the second at the beginning of the prompt causes every request to differ from the first character, so the prefix cache can never hit and everything is billed at full price.79% similarUnverifiedPrompt caching can avoid repeated charges for identical prefixes, because system prompts and retrieved document fragments tend to be highly repetitive across multiple conversation turns.77% similarUnverifiedPrompt caching divides prefixes by 'breakpoints', and the prefix must be byte-for-byte identical to hit the cache, so it is critical to put unstable content such as timestamps and random IDs in the suffix.76% similarUnverifiedPrefix caching depends on strict conditions: the reused portion must be identical from the very first token of the sequence, otherwise the cache is invalidated and the entire segment is recomputed.75% similar
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