Designing the Agent's Brain (Architecture) › A Minimal Agent Architecture (Example: Claude Sonnet 4.5)

import os
import anthropic

class SimpleAgent:
    def __init__(self, model="claude-sonnet-4-5"):
        self.client = anthropic.Anthropic()
        self.model = model
        # State: conversation history
        self.conversation_history = []
        
    def run(self, user_input):
        # Step 1: Receive input
        # Step 2: Update state (add to memory)
        self.conversation_history.append({
            "role": "user",
            "content": user_input
        })
        
        # Step 3 & 4: Decide and act (let the model handle it)
        response = self.client.messages.create(
            model=self.model,
            messages=self.conversation_history,
            max_tokens=1024
        )
        
        # Step 5: Respond
        assistant_message = response.content[0].text
        self.conversation_history.append({
            "role": "assistant",
            "content": assistant_message
        })
        
        return assistant_message

## Try it out
agent = SimpleAgent()
print(agent.run("What's the capital of France?"))
print(agent.run("What did I just ask you?"))