Claude Architect · Lesson

Agent SDK Building Blocks

The pieces that make up an SDK-based agent.

What an SDK Agent Really Is

An Agent SDK agent is not a single API call. It is a loop built from a few reusable pieces that work together.

In this lesson you will learn the core building blocks: the request fields, the tools the model can call, the agentic loop that drives it, and the coordinator + subagents pattern for bigger jobs.

Master these pieces and you can reason about almost any production agent the exam throws at you.

The Request: model, messages, tools

Every turn starts with one request. Its key fields are: model, max_tokens, system, messages, tools, and tool_choice.

The single most important fact: the model keeps NO state between turns. You must send the FULL conversation history in messages on every request. There is no hidden server-side memory.

import anthropic

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-sonnet-4-5",
    max_tokens=1024,
    system="You are a support agent.",
    messages=conversation_history,  # FULL history every turn
    tools=tools,
    tool_choice={"type": "auto"},
)

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