Caching is the fastest way to cut LLM cost — and the fastest way to serve a stale or wrong answer confidently if you cache the wrong thing.
Safe to cache
- Deterministic, fact-stable content: a static FAQ answer, a document summary for a document that never changes.
- Expensive intermediate steps: embeddings for content that doesn't change, retrieval results for a stable query.
Risky to cache
Anything tied to live or personalised data — a user's account balance, today's schedule, current inventory. A cache hit here means confidently wrong, not just slightly stale.
Set a sensible time-to-live for anything that changes, and always include a way to force a cache bypass for debugging. See semantic caching for RAG for the retrieval-specific version of this same trade-off.





