Groundhog Day for AI agents: Prompt caching patterns for using OpenAI models on Amazon Bedrock

This post explains how AI agents resend their full context (tool definitions, instructions, and history) on every turn, and how Amazon Bedrock prompt caching avoids recomputing that prefix by reusing saved key-value state. It covers implicit versus explicit caching, caching conversation history and tool results, handling tool changes with allowed_tools and additional_tools, sharing cached prefixes across subagents and new sessions via prompt_cache_key, and monitoring cache reads and writes through response usage and CloudWatch.