The code execution tool allows Claude to execute Python code in a secure, sandboxed environment. Claude can analyze data, create visualizations, perform complex calculations, and process uploaded files directly within the API conversation.
The code execution tool is currently in beta.This feature requires the beta header: "anthropic-beta": "code-execution-2025-05-22"

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Supported models

The code execution tool is available on:
  • Claude Opus 4.1 (claude-opus-4-1-20250805)
  • Claude Opus 4 (claude-opus-4-20250514)
  • Claude Sonnet 4 (claude-sonnet-4-20250514)
  • Claude Sonnet 3.7 (claude-3-7-sonnet-20250219)
  • Claude Haiku 3.5 (claude-3-5-haiku-latest)

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Quick start

Here’s a simple example that asks Claude to perform a calculation: 
curl https://api.anthropic.com/v1/messages \
    --header "x-api-key: $ANTHROPIC_API_KEY" \
    --header "anthropic-version: 2023-06-01" \
    --header "anthropic-beta: code-execution-2025-05-22" \
    --header "content-type: application/json" \
    --data '{
        "model": "claude-opus-4-1-20250805",
        "max_tokens": 4096,
        "messages": [
            {
                "role": "user",
                "content": "Calculate the mean and standard deviation of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]"
            }
        ],
        "tools": [{
            "type": "code_execution_20250522",
            "name": "code_execution"
        }]
    }'

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How code execution works

When you add the code execution tool to your API request:
  1. Claude evaluates whether code execution would help answer your question
  2. Claude writes and executes Python code in a secure sandbox environment
  3. Code execution may occur multiple times throughout a single request
  4. Claude provides results with any generated charts, calculations, or analysis

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Tool definition

The code execution tool requires no additional parameters:
JSON
{
  "type": "code_execution_20250522",
  "name": "code_execution"
}

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Response format

Here’s an example response with code execution: 
{
  "role": "assistant",
  "container": {
    "id": "container_011CPR5CNjB747bTd36fQLFk",
    "expires_at": "2025-05-23T21:13:31.749448Z"
  },
  "content": [
    {
      "type": "text",
      "text": "I'll calculate the mean and standard deviation for you."
    },
    {
      "type": "server_tool_use",
      "id": "srvtoolu_01A2B3C4D5E6F7G8H9I0J1K2",
      "name": "code_execution",
      "input": {
        "code": "import numpy as np\ndata = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\nmean = np.mean(data)\nstd = np.std(data)\nprint(f\"Mean: {mean}\")\nprint(f\"Standard deviation: {std}\")"
      }
    },
    {
      "type": "code_execution_tool_result",
      "tool_use_id": "srvtoolu_01A2B3C4D5E6F7G8H9I0J1K2",
      "content": {
        "type": "code_execution_result",
        "stdout": "Mean: 5.5\nStandard deviation: 2.8722813232690143\n",
        "stderr": "",
        "return_code": 0
      }
    },
    {
      "type": "text",
      "text": "The mean of the dataset is 5.5 and the standard deviation is approximately 2.87."
    }
  ],
  "id": "msg_01BqK2v4FnRs4xTjgL8EuZxz",
  "model": "claude-opus-4-1-20250805",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 45,
    "output_tokens": 187,
  }
}

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Results

Code execution results include:
  • stdout: Output from print statements and successful execution
  • stderr: Error messages if code execution fails
  • return_code (0 for success, non-zero for failure)
{
  "type": "code_execution_tool_result",
  "tool_use_id": "srvtoolu_01ABC123",
  "content": {
    "type": "code_execution_result",
    "stdout": "",
    "stderr": "NameError: name 'undefined_variable' is not defined",
    "return_code": 1
  }
}

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Errors

If there is an error using the tool there will be a code_execution_tool_result_error 
{
  "type": "code_execution_tool_result",
  "tool_use_id": "srvtoolu_01VfmxgZ46TiHbmXgy928hQR",
  "content": {
    "type": "code_execution_tool_result_error",
    "error_code": "unavailable"
  }
}
Possible errors include
  • unavailable: The code execution tool is unavailable
  • code_execution_exceeded: Execution time exceeded the maximum allowed
  • container_expired: The container is expired and not available

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pause_turn stop reason

The response may include a pause_turn stop reason, which indicates that the API paused a long-running turn. You may provide the response back as-is in a subsequent request to let Claude continue its turn, or modify the content if you wish to interrupt the conversation.

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Working with Files in Code Execution

Code execution can analyze files uploaded via the Files API, such as CSV files, Excel files, and other data formats. This allows Claude to read, process, and generate insights from your data. You can pass multiple files per request.
Using the Files API with Code Execution requires two beta headers: "anthropic-beta": "code-execution-2025-05-22,files-api-2025-04-14"

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Supported file types

The Python environment is capable of working with but not limited to the following file types
  • CSV
  • Excel (.xlsx, .xls)
  • JSON
  • XML
  • Images (JPEG, PNG, GIF, WebP)
  • Text files (.txt, .md, .py, etc)

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Loading files for code execution

  1. Upload your file using the Files API
  2. Reference the file in your message using a container_upload content block
  3. Include the code execution tool in your API request
# First, upload a file
curl https://api.anthropic.com/v1/files \
    --header "x-api-key: $ANTHROPIC_API_KEY" \
    --header "anthropic-version: 2023-06-01" \
    --header "anthropic-beta: files-api-2025-04-14" \
    --form 'file=@"data.csv"' \

# Then use the file_id with code execution
curl https://api.anthropic.com/v1/messages \
    --header "x-api-key: $ANTHROPIC_API_KEY" \
    --header "anthropic-version: 2023-06-01" \
    --header "anthropic-beta: code-execution-2025-05-22,files-api-2025-04-14" \
    --header "content-type: application/json" \
    --data '{
        "model": "claude-opus-4-1-20250805",
        "max_tokens": 4096,
        "messages": [{
            "role": "user",
            "content": [
                {"type": "text", "text": "Analyze this CSV data"},
                {"type": "container_upload", "file_id": "file_abc123"}
            ]
        }],
        "tools": [{
            "type": "code_execution_20250522",
            "name": "code_execution"
        }]
    }'

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Retrieving files created by code execution

When Claude creates files during code execution (e.g., saving matplotlib plots, generating CSVs), you can retrieve these files using the Files API: 
from anthropic import Anthropic

# Initialize the client
client = Anthropic()

# Request code execution that creates files
response = client.beta.messages.create(
    model="claude-opus-4-1-20250805",
    betas=["code-execution-2025-05-22", "files-api-2025-04-14"],
    max_tokens=4096,
    messages=[{
        "role": "user",
        "content": "Create a matplotlib visualization and save it as output.png"
    }],
    tools=[{
        "type": "code_execution_20250522",
        "name": "code_execution"
    }]
)

# Extract file IDs from the response
def extract_file_ids(response):
    file_ids = []
    for item in response.content:
        if item.type == 'code_execution_tool_result':
            content_item = item.content
            if content_item.get('type') == 'code_execution_result':
                for file in content_item.get('content', []):
                    file_ids.append(file['file_id'])
    return file_ids

# Download the created files
for file_id in extract_file_ids(response):
    file_metadata = client.beta.files.retrieve_metadata(file_id)
    file_content = client.beta.files.download(file_id)
    file_content.write_to_file(file_metadata.filename)
    print(f"Downloaded: {file_metadata.filename}")

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Containers

The code execution tool runs in a secure, containerized environment designed specifically for Python code execution.

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Runtime environment

  • Python version: 3.11.12
  • Operating system: Linux-based container
  • Architecture: x86_64 (AMD64)

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Resource limits

  • Memory: 1GiB RAM
  • Disk space: 5GiB workspace storage
  • CPU: 1 CPU

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Networking and security

  • Internet access: Completely disabled for security
  • External connections: No outbound network requests permitted
  • Sandbox isolation: Full isolation from host system and other containers
  • File access: Limited to workspace directory only
  • Workspace scoping: Like Files, containers are scoped to the workspace of the API key
  • Expiration: Containers expire 1 hour after creation

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Pre-installed libraries

The sandboxed Python environment includes these commonly used libraries:
  • Data Science: pandas, numpy, scipy, scikit-learn, statsmodels
  • Visualization: matplotlib
  • File Processing: pyarrow, openpyxl, xlrd, pillow
  • Math & Computing: sympy, mpmath
  • Utilities: tqdm, python-dateutil, pytz, joblib

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Container reuse

You can reuse an existing container across multiple API requests by providing the container ID from a previous response. This allows you to maintain created files between requests.

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Example

import os
from anthropic import Anthropic

# Initialize the client
client = Anthropic(
    api_key=os.getenv("ANTHROPIC_API_KEY")
)

# First request: Create a file with a random number
response1 = client.beta.messages.create(
    model="claude-opus-4-1-20250805",
    betas=["code-execution-2025-05-22"],
    max_tokens=4096,
    messages=[{
        "role": "user",
        "content": "Write a file with a random number and save it to '/tmp/number.txt'"
    }],
    tools=[{
        "type": "code_execution_20250522",
        "name": "code_execution"
    }]
)

# Extract the container ID from the first response
container_id = response1.container.id

# Second request: Reuse the container to read the file
response2 = client.beta.messages.create(
    container=container_id,  # Reuse the same container
    model="claude-opus-4-1-20250805",
    betas=["code-execution-2025-05-22"],
    max_tokens=4096,
    messages=[{
        "role": "user",
        "content": "Read the number from '/tmp/number.txt' and calculate its square"
    }],
    tools=[{
        "type": "code_execution_20250522",
        "name": "code_execution"
    }]
)

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Streaming

With streaming enabled, you’ll receive code execution events as they occur: 
event: content_block_start
data: {"type": "content_block_start", "index": 1, "content_block": {"type": "server_tool_use", "id": "srvtoolu_xyz789", "name": "code_execution"}}

// Code execution streamed
event: content_block_delta
data: {"type": "content_block_delta", "index": 1, "delta": {"type": "input_json_delta", "partial_json": "{\"code\":\"import pandas as pd\\ndf = pd.read_csv('data.csv')\\nprint(df.head())\"}"}}

// Pause while code executes

// Execution results streamed
event: content_block_start
data: {"type": "content_block_start", "index": 2, "content_block": {"type": "code_execution_tool_result", "tool_use_id": "srvtoolu_xyz789", "content": {"stdout": "   A  B  C\n0  1  2  3\n1  4  5  6", "stderr": ""}}}

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Batch requests

You can include the code execution tool in the Messages Batches API. Code execution tool calls through the Messages Batches API are priced the same as those in regular Messages API requests.

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Usage and pricing

The code execution tool usage is tracked separately from token usage. Execution time is a minimum of 5 minutes. If files are included in the request, execution time is billed even if the tool is not used due to files being preloaded onto the container. Pricing: $0.05 per session-hour.