claude-code-model 0.4.2

Pydantic AI model adapter for Claude Code CLI

claude-code-model

Use Pydantic AI with your Claude Max subscription instead of paying per token.

A drop-in replacement that routes Pydantic AI through Claude Code CLI. Same code, same features, zero API costs.

The Problem

You want to use Pydantic AI for type-safe AI agents, but the API costs add up:

# This costs $3-15 per 1M tokens
from pydantic_ai.models.anthropic import AnthropicModel
model = AnthropicModel("claude-sonnet-4-20250514")

Meanwhile, your Claude Max subscription ($100-200/month) gives you unlimited Claude access via CLI, but no programmatic interface for building agents.

The Solution

claude-code-model bridges this gap. Change 2 lines and your Pydantic AI code runs on your Max subscription:

- from pydantic_ai.models.anthropic import AnthropicModel
- model = AnthropicModel("claude-sonnet-4-20250514")
+ from claude_code_model import ClaudeCodeModel
+ model = ClaudeCodeModel(model="sonnet")

That's it. Your agents, tools, schemas, and prompts stay exactly the same.

Quick Comparison

Feature	Pydantic AI + API	claude-code-model
Cost	$3-15/M tokens	$0 (Max subscription)
Structured output	Yes	Yes
Tool calling	Yes	Yes
Vision / images	Yes	Yes (binary only)
Type safety	Yes	Yes
Streaming	Yes	No
Concurrent requests	Yes	No
Migration effort	—	2 lines

Installation

# 1. Install Claude Code CLI (requires Node.js)
npm install -g @anthropic-ai/claude-code

# 2. Login to Claude
claude auth

# 3. Install this package
pip install claude-code-model

Usage

Basic Example

from pydantic import BaseModel
from pydantic_ai import Agent
from claude_code_model import ClaudeCodeModel

class MovieReview(BaseModel):
    title: str
    rating: int  # 1-10
    summary: str

agent = Agent(
    ClaudeCodeModel(),
    output_type=MovieReview,
    system_prompt="You are a film critic. Review movies concisely."
)

result = agent.run_sync("Review: The Matrix (1999)")
print(f"{result.output.title}: {result.output.rating}/10")
# The Matrix: 9/10

With Tools

from pydantic_ai import Agent
from claude_code_model import ClaudeCodeModel

agent = Agent(ClaudeCodeModel())

@agent.tool_plain
def get_weather(city: str) -> str:
    """Get current weather for a city."""
    # Your implementation here
    return f"Weather in {city}: 72°F, sunny"

result = agent.run_sync("What's the weather in Tokyo?")
# Agent calls get_weather("Tokyo") and uses the result

Vision / Image Input

from pydantic_ai import Agent
from pydantic_ai.messages import BinaryContent
from claude_code_model import ClaudeCodeModel

agent = Agent(
    ClaudeCodeModel(),
    system_prompt="Describe images concisely.",
)

# Load an image as binary content
image = BinaryContent.from_path("photo.jpg")

result = agent.run_sync(["What's in this image?", image])
print(result.output)

Images are sent to the CLI via stdin JSON format using --input-format stream-json. Multiple images can be passed in a single message.

Multi-Agent Systems

from pydantic_ai import Agent
from claude_code_model import ClaudeCodeModel

# Fast agent for simple tasks
fast_agent = Agent(
    ClaudeCodeModel(model="haiku"),
    system_prompt="Quick factual responses only."
)

# Powerful agent for complex reasoning
smart_agent = Agent(
    ClaudeCodeModel(model="sonnet"),
    system_prompt="Deep analysis and reasoning."
)

# Agents can delegate to each other via tools
@smart_agent.tool_plain
async def quick_lookup(query: str) -> str:
    """Delegate simple lookups to the fast agent."""
    result = await fast_agent.run(query)
    return result.output

See examples/multi_agent_comparison.py for a complete multi-agent pipeline.

Migration from Pydantic AI

Step 1: Install

pip install claude-code-model

Step 2: Replace Import

# Before
from pydantic_ai.models.anthropic import AnthropicModel

# After
from claude_code_model import ClaudeCodeModel

Step 3: Replace Model

# Before
model = AnthropicModel("claude-sonnet-4-20250514")

# After
model = ClaudeCodeModel(model="sonnet")  # or "opus", "haiku"

That's It

All your existing code works unchanged:

# This code is IDENTICAL for both API and CLI
agent = Agent(
    model,  # <-- Only this changes
    output_type=MySchema,
    system_prompt="Your prompt here",
    retries=3,
)

@agent.tool_plain
def my_tool(arg: str) -> str:
    return do_something(arg)

result = agent.run_sync("Your query")
print(result.output)  # Typed result

Configuration

from claude_code_model import ClaudeCodeModel

model = ClaudeCodeModel(
    model="sonnet",    # "sonnet" (default), "opus", or "haiku"
    timeout=30,        # Seconds per CLI request (default: 30)
    verbose=False,     # Enable debug logging
)

Model Selection

Model	Speed	Capability	Use Case
haiku	Fast	Good	Simple tasks, quick lookups
sonnet	Medium	Great	Most tasks (default)
opus	Slow	Best	Complex reasoning, analysis

Debug Mode

model = ClaudeCodeModel(verbose=True)

Shows request/response timing, prompts sent, tool calls detected, and JSON extraction status.

How It Works

Your Code                      claude-code-model              Claude CLI
─────────────────────────────────────────────────────────────────────────
agent.run_sync("prompt")  →   Build prompt string      →   claude -p "..."
                              Add tool definitions          --model sonnet
                              Add JSON schema

result.output             ←   Parse response           ←   {"rating": 9, ...}
                              Extract JSON
                              Validate with Pydantic

The adapter:

1. Converts Pydantic AI messages → single prompt string
2. Adds tool definitions with format instructions
3. Adds JSON schema requirements for structured output
4. Calls claude -p "prompt" --model sonnet via subprocess
5. Parses response for tool calls or JSON output
6. Returns typed ModelResponse to Pydantic AI

Examples

Run the examples to see it in action:

# Basic structured output
uv run python examples/simple.py

# Interactive tool usage
uv run python examples/with_tools.py

# Multi-agent pipeline with comparison
uv run python examples/multi_agent_comparison.py

Limitations

No streaming — CLI doesn't support streaming well. Each request returns complete.

No concurrent requests — Run one request at a time. CLI sessions don't parallelize.

No token counting — CLI doesn't report token usage. result.usage returns zeros.

Image URLs not supported — Only binary image data (BinaryContent) is supported. ImageUrl references are not sent to the CLI.

Slower than API — Each CLI invocation takes 2-10 seconds overhead. Multi-step tasks with tool calls take longer.

Tool calling is prompt-based — Unlike native API tools, this adapter instructs Claude to output TOOL_CALL: name({args}) format. Works well but occasionally needs retries. Use retries=3-5 on your agents.

Exceptions

from claude_code_model import (
    ClaudeCodeError,           # Base exception
    ClaudeCodeNotFoundError,   # CLI not installed
    ClaudeCodeTimeoutError,    # Request timed out
    ClaudeCodeExecutionError,  # CLI returned error
)

Development

git clone https://github.com/yourusername/claude-code-model.git
cd claude-code-model
uv sync

# Run tests
uv run pytest

# Type check
uv run mypy src/

# Lint
uv run ruff check src/ tests/

Requirements

• Python 3.11+
• Claude Code CLI installed and authenticated
• Claude Max subscription (for unlimited CLI access)
• pydantic-ai >= 0.1.0
• pydantic >= 2.0.0

License

MIT — see LICENSE.

Links

• Pydantic AI Documentation
• Claude Code
• Development Guide

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Disclaimer: Unofficial adapter, not affiliated with Anthropic. Use in accordance with Claude's Terms of Service.