Semantic Caching vs Prompt Caching: Which Saves More?

Prompt caching discounts the repeated start of a prompt. Semantic caching skips the model call entirely when a similar question was already answered.

Quick answer

Prompt caching is safe everywhere and cuts input cost. Semantic caching can remove whole calls, but only belongs on routes where a shared answer is correct.

Prompt caching

The provider reuses work for an identical prompt prefix and bills it at a lower cached rate. The model still answers every request, so answers are unchanged. It's the first lever to switch on.

Semantic caching

A gateway stores answers and serves a stored answer when a new request is close enough in meaning. It saves the whole call, input and output, but it's a product decision: the answer is reused.

When semantic caching is unsafe

Personal or account-specific answers.
Time-sensitive information.
Answers that must reflect the latest data.
Anything regulated where a reused answer could be wrong for someone.

Where it works

FAQs, documentation questions, product descriptions and other places where many users ask the same thing and the right answer is the same.

Use both

Prompt caching everywhere, semantic caching only on approved routes, with conservative matching and expiry. That's how apicuts runs it: semantic caching is off by default and switched on per route. See caching.

Frequently asked questions

Is semantic caching safe?

On routes where many users should get the same answer, with conservative matching and expiry. Not for personal or time-sensitive answers.

Which saves more, semantic or prompt caching?

Semantic caching saves more per hit because it skips the call, but prompt caching applies to far more traffic safely.

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