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This guide shows you how to build an agent using Anthropic’s Claude models with the Claude Agent SDK, which provides tool use capabilities out of the box.

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Prerequisites

  • Python 3.9+
  • cycls package installed
  • Anthropic API key
  • Docker installed (for local testing)
pip install cycls

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Basic Claude Agent

Create a file called app.py: 
import cycls

@cycls.app(pip=["anthropic"], copy=[".env"])
async def app(context):
    from anthropic import AsyncAnthropic

    client = AsyncAnthropic()

    async with client.messages.stream(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        messages=context.messages
    ) as stream:
        async for text in stream.text_stream:
            yield text

app.local()
Create a .env file: 
ANTHROPIC_API_KEY=sk-ant-...
Run the agent: 
python app.py

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Claude Agent SDK with Tools

For more advanced use cases, you can use the Claude Agent SDK which provides built-in tool support: 
import cycls

@cycls.app(pip=["claude-agent-sdk"], copy=[".env"])
async def app(context):
    from claude_agent_sdk import (
        ClaudeSDKClient,
        ClaudeAgentOptions,
        AssistantMessage,
        TextBlock,
        ToolUseBlock,
        ThinkingBlock,
        ResultMessage,
    )

    async with ClaudeSDKClient(
        options=ClaudeAgentOptions(
            allowed_tools=["Read", "Edit", "Glob", "Grep", "Bash", "WebSearch"],
            permission_mode="acceptEdits",
        )
    ) as client:
        await client.query(context.last_message)

        async for message in client.receive_response():
            if isinstance(message, AssistantMessage):
                for block in message.content:
                    if isinstance(block, TextBlock):
                        yield block.text
                    elif isinstance(block, ThinkingBlock):
                        yield {"type": "thinking", "thinking": block.thinking}
                    elif isinstance(block, ToolUseBlock):
                        yield {"type": "thinking", "thinking": f"Using tool: {block.name}"}

            elif isinstance(message, ResultMessage):
                yield {"type": "thinking", "thinking": "Tool completed"}

app.local()
This example:
  • Uses the Claude Agent SDK for tool-based interactions
  • Streams text responses directly to the user
  • Shows thinking blocks for reasoning visibility
  • Displays tool usage as thinking bubbles

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Configuration

Create a .env file with your API key: 
ANTHROPIC_API_KEY=sk-ant-...

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Deploy to Cloud

import cycls
import os

cycls.api_key = os.getenv("CYCLS_API_KEY")

@cycls.app(pip=["anthropic"], copy=[".env"])
async def app(context):
    from anthropic import AsyncAnthropic

    client = AsyncAnthropic()

    async with client.messages.stream(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        messages=context.messages
    ) as stream:
        async for text in stream.text_stream:
            yield text

app.deploy()