Prompt Caching for AI Agents: Save 70%+ on API Costs
Cut AI agent API costs by 70–90% with prompt caching. Real pricing data for OpenAI, Anthropic & Google. Code examples and proven patterns inside.
Frequently Asked Questions
What is prompt caching for AI agents?
Prompt caching stores the computed representation of your AI agent's system prompt so the LLM doesn't reprocess it on every request. Providers like Anthropic, OpenAI, and Google offer 50–90% discounts on cached input tokens. For agents with large system prompts, caching pays for itself on the second request. See our [cost optimization guide](/blog/ai-agent-cost-optimization/) for more tactics.
How much does prompt caching save on AI agent costs?
Real-world deployments report 41–80% total cost reduction from prompt caching alone. Anthropic charges 90% less for cached tokens, OpenAI gives 50–75% off, and Google Gemini charges 90% less for cached reads. The savings depend on your cache hit rate, which improves when you keep system prompts static and place dynamic content last.
Does prompt caching work automatically?
It depends on the provider. OpenAI caches automatically for any prompt over 1,024 tokens — no code changes needed. Anthropic requires explicit cache breakpoints via the API (or automatic mode with a single flag). Google Gemini offers both implicit (automatic) and explicit caching. Check our [prompt engineering guide](/blog/ai-agent-prompt-engineering/) for structuring prompts to maximize cache hits.
What is the minimum prompt size for caching?
Anthropic requires 1,024–4,096 tokens minimum depending on the model. OpenAI requires at least 1,024 tokens. Google Gemini requires 1,024 tokens for implicit caching and 32,768 tokens for explicit caching. Most AI agent system prompts (with tool definitions) easily exceed these thresholds.
How long do cached prompts last?
Anthropic caches last 5 minutes by default (refreshed on each hit), with an optional 1-hour TTL at higher write cost. OpenAI caches persist for 5–10 minutes of inactivity and always clear within 1 hour. Google Gemini's explicit caches have a configurable TTL (default 1 hour) with per-hour storage fees.