Move your static prefix first and watch cache hit rate jump from 23% to 71%

This is the "do it today" story, and it's the cheapest cost cut on this entire list. Most LLM cost dashboards don't even show cache hit rate, yet it's the single biggest lever you've got. One production team moved a roughly 300-token user-context block out of the system prompt and to the start of the user turn, and watched cache hit rate go from 23% to 71%. Zero API changes, no latency risk, per AgentMarketCap. That's a 3x improvement in cached-token reuse from rearranging where text sits.

Here's the mechanic. Prefix caching keys on a byte-identical prefix. The moment something dynamic appears early in your prompt, everything after it is uncacheable, because the prefix no longer matches. People stuff per-request context (user data, retrieved snippets, timestamps) into the system prompt because that's where "context" feels like it belongs. That single dynamic block poisons the cache for the entire stable instruction set sitting behind it. Move the static instructions to the front, push the mutable state to the back, and the expensive stable part stays cached across every call.

You can go further. Explicitly marking segments with cache_control breakpoints (system prompt cached separately from tool definitions, long reference docs cached, dynamic user context left uncached) delivers a 2-5x hit-rate improvement over automatic caching, for one or two hours of work (SurePrompts). And when user phrasing varies, cache the plan, not the tokens: semantic caching (vCache, Feb 2026) serves a cached response when embedding similarity clears a threshold, and agentic plan caching skips re-planning for repeated task shapes entirely (Harness Engineering Academy).

This connects straight back to story one. June 15, your headless agents get metered at full API rates. A 3x cache hit rate improvement is a direct 3x cut on the cached portion of that bill. The teams that measure cache hit rate are about to have a structural cost advantage over the teams that don't. Treat your system prompt as a versioned artifact and assert a minimum cache hit rate in CI so it can't silently degrade as your codebase grows. That last part is the discipline most people skip, and it's why their hit rate quietly rots back to 23% three months later.

What to do: instrument cache hit rate this week, before the metering change. If you've never measured it, you're almost certainly leaving the easiest cost win on the table.