Most LLM wrapper libraries do three things: send a request, get a response, done. But a true Agent goes further — it decides whether to call tools, executes them, feeds the results back to the LLM, and loops until it arrives at a final answer. This loop is the Agent Loop . This article analyzes the Open Agent SDK (Swift) Agent Loop implementation — how it uses native Swift concurrency to run the entire cycle in-process. What Is the Agent Loop? In one sentence: user sends a prompt → LLM returns a response → if the LLM wants to call tools, execute them → feed tool results back to the LLM → repeat until the LLM says "I'm done" .…