In vLLM v0.23.0, vllm:prefix_cache_hits is the token numerator for a same-label, same-window prefix-cache hit ratio.

Metric

Applies when

Evidence

Does not establish

• a workload-independent healthy threshold
• semantics in any vLLM version other than v0.23.0

Guards

• vllm_version = v0.23.0
• metric_name = vllm:prefix_cache_hits

Freshness

Pinned release-tag semantics; do not carry to another version without continuity evidence.