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Cost
Cached input
A token sent to the model that the provider has already processed, billed at a discount.
When you send the same prompt prefix repeatedly (system prompt, retrieved-doc context, conversation history), the provider can cache its KV-state internally and bill those tokens at a fraction of the regular rate — typically 10-25%. Aggressive prompt caching is the highest-leverage cost optimization in production AI: 60-85% input-cost reduction with zero behavior change. Requires structuring prompts so the stable parts come first.
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