Prompt Caching: What It Saves You and When It's Worth Setting Up

Prompt caching lets a provider skip reprocessing the parts of your prompt that haven't changed since the last call — a long system prompt, a big document, a large set of few-shot examples — and only pay full cost for what's new. The savings show up as both lower cost and lower latency on the cached portion. It's worth setting up when: - The same large block of context (a system prompt, a knowledge document, a tool schema) is sent on every call in a session or a high-volume workflow. - That block is meaningfully large — the savings on a two-sentence system prompt aren't worth the added complexity. - Requests happen close enough together in time to actually hit the cache (caches expire; a job that runs once a day per user won't benefit the way a chat session will). It's not worth the complexity when your prompts are short, mostly unique per request, or your traffic is too low/sparse for anything to still be cached by the time the next request arrives. Structure the prompt with the stable, cacheable part first and the request-specific part last — most caching implementations only benefit from a shared prefix, so a variable inserted early in the prompt defeats caching for everything after it.