# Prompt caching: what each client sends and what Usage reports

A. Anthropic: the strategy decides whether the system prompt carries a cache breakpoint
  strategy NONE         system is a plain string
    call 1: promptTokens=6014 cacheRead=0 cacheWrite=0
    call 2: promptTokens=6014 cacheRead=0 cacheWrite=0
  strategy SYSTEM_ONLY  system is a list of 1 block(s), cache_control on block 0: true
    call 1: promptTokens=3 cacheRead=0 cacheWrite=6011
    call 2: promptTokens=3 cacheRead=6011 cacheWrite=0

B. OpenAI and Gemini: nothing to switch on, but the order of the text decides the hit
  OPENAI  timestamp AFTER the policy:        call 1 cacheRead=0     call 2 cacheRead=6016 of 6019 prompt tokens
  OPENAI  timestamp BEFORE the policy:       call 1 cacheRead=0     call 2 cacheRead=0 of 6019 prompt tokens
  GEMINI  timestamp AFTER the policy:        call 1 cacheRead=0     call 2 cacheRead=6016 of 6019 prompt tokens
  GEMINI  timestamp BEFORE the policy:       call 1 cacheRead=0     call 2 cacheRead=0 of 6019 prompt tokens

C. A prompt below the vendor's minimum: the client still asks, the vendor does not cache
  Anthropic SYSTEM_ONLY, 847-character policy: cache_control sent=true, cacheRead=0 cacheWrite=0