Model Factory - DeerFlow

DeerFlow’s model factory (backend/src/models/factory.py) provides reflection-based model instantiation from configuration files, enabling dynamic provider support without hardcoding imports. The factory handles thinking modes, vision capabilities, and runtime parameter overrides.

Core Function: create_chat_model()

from langchain.chat_models import BaseChatModel

def create_chat_model(
    name: str | None = None,
    thinking_enabled: bool = False,
    **kwargs
) -> BaseChatModel:
    """Create a chat model instance from config.
    
    Args:
        name: Model name from config. If None, uses first model in config.
        thinking_enabled: Enable extended thinking mode (if model supports it).
        **kwargs: Runtime overrides for model parameters.
    
    Returns:
        Instantiated chat model.
    """

Location: backend/src/models/factory.py:11-64

Model Configuration

config.yaml Structure

models:
  - name: gpt-4o
    display_name: GPT-4 Optimized
    description: OpenAI's fastest flagship model
    use: langchain_openai:ChatOpenAI
    model: gpt-4o
    temperature: 0.7
    supports_thinking: true
    supports_reasoning_effort: true
    supports_vision: true
    when_thinking_enabled:
      extra_body:
        thinking:
          type: enabled
          budget_tokens: 10000
      reasoning_effort: high
  
  - name: claude-sonnet
    display_name: Claude 3.5 Sonnet
    description: Anthropic's balanced model
    use: langchain_anthropic:ChatAnthropic
    model: claude-3-5-sonnet-20241022
    temperature: 0.7
    max_tokens: 4096
    supports_thinking: true
    supports_vision: true
    when_thinking_enabled:
      extra_body:
        thinking:
          type: enabled
          budget_tokens: 10000
  
  - name: deepseek-chat
    display_name: DeepSeek Chat
    description: DeepSeek's reasoning model
    use: src.models.patched_deepseek:PatchedChatDeepSeek
    model: deepseek-chat
    base_url: $DEEPSEEK_BASE_URL
    api_key: $DEEPSEEK_API_KEY
    temperature: 1.0
    supports_thinking: false
    supports_vision: false

Field Reference

Core Fields

name (required): Unique identifier for model selection
display_name: Human-readable name for UI
description: Short description of model capabilities
use (required): Python import path for model class (e.g., langchain_openai:ChatOpenAI)

Capability Flags

supports_thinking: Model supports extended thinking/reasoning modes
supports_reasoning_effort: Model supports OpenAI’s reasoning_effort parameter
supports_vision: Model can process images (enables ViewImageMiddleware)

Provider Parameters

All additional fields passed to model constructor:

# OpenAI-specific
model: gpt-4o
temperature: 0.7
max_tokens: 4096

# Anthropic-specific  
model: claude-3-5-sonnet-20241022
max_tokens: 4096

# Custom base URL
base_url: https://api.custom-provider.com
api_key: $API_KEY  # Resolved from environment

when_thinking_enabled

Overrides applied when thinking_enabled=True:

when_thinking_enabled:
  extra_body:  # OpenAI extended thinking
    thinking:
      type: enabled
      budget_tokens: 10000
  reasoning_effort: high  # o1 models

Reflection-Based Instantiation

The factory uses the reflection system to dynamically load model classes:

from src.reflection import resolve_class

# Load model config
config = get_app_config()
model_config = config.get_model_config(name or config.models[0].name)

# Resolve class via reflection
model_class = resolve_class(model_config.use, BaseChatModel)
# e.g., resolve_class("langchain_openai:ChatOpenAI", BaseChatModel)
# → imports langchain_openai, returns ChatOpenAI class, validates subclass

Benefits:

No hardcoded imports (from langchain_openai import ChatOpenAI)
Add new providers without code changes (just update config.yaml)
Clear error messages for missing dependencies

Thinking Mode Support

Enabling Thinking

# Default model without thinking
model = create_chat_model()

# Enable thinking mode
model = create_chat_model(thinking_enabled=True)

# Specific model with thinking
model = create_chat_model(name="gpt-4o", thinking_enabled=True)

Implementation

def create_chat_model(name=None, thinking_enabled=False, **kwargs):
    # ...
    model_settings = model_config.model_dump(
        exclude_none=True,
        exclude={
            "use", "name", "display_name", "description",
            "supports_thinking", "supports_reasoning_effort",
            "when_thinking_enabled", "supports_vision"
        }
    )
    
    # Apply thinking overrides
    if thinking_enabled and model_config.when_thinking_enabled:
        if not model_config.supports_thinking:
            raise ValueError(
                f"Model {name} does not support thinking. "
                "Set `supports_thinking: true` in config.yaml"
            )
        model_settings.update(model_config.when_thinking_enabled)
    
    # Disable thinking explicitly if not requested
    if not thinking_enabled and model_config.when_thinking_enabled:
        if model_config.when_thinking_enabled.get("extra_body", {}).get("thinking"):
            kwargs.update({"extra_body": {"thinking": {"type": "disabled"}}})
            kwargs.update({"reasoning_effort": "minimal"})
    
    # Handle reasoning_effort for models that don't support it
    if not model_config.supports_reasoning_effort:
        kwargs.update({"reasoning_effort": None})
    
    # Instantiate model
    model_instance = model_class(**kwargs, **model_settings)
    return model_instance

Thinking Configurations

OpenAI Extended Thinking

when_thinking_enabled:
  extra_body:
    thinking:
      type: enabled
      budget_tokens: 10000  # Max tokens for thinking phase

Behavior: Model generates hidden thinking before response.

OpenAI o1 Reasoning Effort

supports_reasoning_effort: true
when_thinking_enabled:
  reasoning_effort: high  # low | medium | high

Behavior: Controls o1 model’s reasoning intensity.

Anthropic Extended Thinking

when_thinking_enabled:
  extra_body:
    thinking:
      type: enabled
      budget_tokens: 10000

Behavior: Claude uses <thinking> tags in response.

Vision Support

Models with supports_vision: true enable vision-specific features:

Configuration

models:
  - name: gpt-4o
    supports_vision: true
    # ...
  
  - name: claude-sonnet
    supports_vision: true
    # ...
  
  - name: gpt-4o-mini
    supports_vision: false  # Text-only
    # ...

Impact on Agent

Middleware Chain (backend/src/agents/lead_agent/agent.py:236-241):

def _build_middlewares(config, model_name, agent_name=None):
    # ...
    
    # Add ViewImageMiddleware only if model supports vision
    app_config = get_app_config()
    model_config = app_config.get_model_config(model_name)
    if model_config and model_config.supports_vision:
        middlewares.append(ViewImageMiddleware())
    
    # ...

Tool Injection (backend/src/tools/__init__.py):

def get_available_tools(model_name=None, **kwargs):
    tools = [...]
    
    # Add view_image tool only for vision models
    model_config = get_app_config().get_model_config(model_name)
    if model_config and model_config.supports_vision:
        from src.tools.builtins import view_image_tool
        tools.append(view_image_tool)
    
    return tools

Runtime Parameter Overrides

Via Keyword Arguments

# Override temperature
model = create_chat_model(
    name="gpt-4o",
    temperature=0.9  # Override config's 0.7
)

# Override max_tokens
model = create_chat_model(
    name="claude-sonnet",
    max_tokens=8000  # Override config's 4096
)

# Add custom parameters
model = create_chat_model(
    name="gpt-4o",
    top_p=0.95,
    frequency_penalty=0.5
)

Merge Behavior

# Config settings
model_settings = {
    "model": "gpt-4o",
    "temperature": 0.7,
    "max_tokens": 4096
}

# Runtime overrides
kwargs = {
    "temperature": 0.9,
    "top_p": 0.95
}

# Final parameters
final = {**model_settings, **kwargs}
# → {
#     "model": "gpt-4o",
#     "temperature": 0.9,  # Overridden
#     "max_tokens": 4096,
#     "top_p": 0.95        # Added
# }

model_instance = model_class(**final)

Environment Variable Resolution

Config values starting with $ are resolved from environment:

models:
  - name: custom-model
    use: langchain_openai:ChatOpenAI
    base_url: $CUSTOM_BASE_URL
    api_key: $CUSTOM_API_KEY
    default_headers:
      X-Custom-Header: $CUSTOM_HEADER

Resolution (handled by Pydantic config loader):

import os

# Before resolution (from YAML)
config_data = {
    "base_url": "$CUSTOM_BASE_URL",
    "api_key": "$CUSTOM_API_KEY"
}

# After resolution (automatic)
resolved_config = {
    "base_url": os.getenv("CUSTOM_BASE_URL"),
    "api_key": os.getenv("CUSTOM_API_KEY")
}

Missing Environment Variables: Raise error at startup.

Error Handling

Missing Model

model = create_chat_model(name="nonexistent")
# ValueError: Model nonexistent not found in config

Missing Provider

# config.yaml
models:
  - name: gemini
    use: langchain_google_genai:ChatGoogleGenerativeAI
    # ... but langchain-google-genai not installed

model = create_chat_model(name="gemini")
# ImportError: Could not import module langchain_google_genai.
#              Missing dependency 'google-generativeai'.
#              Install with `uv add langchain-google-genai`, then restart.

Actionable Hints (from reflection system):

MODULE_TO_PACKAGE_HINTS = {
    "langchain_google_genai": "langchain-google-genai",
    "langchain_anthropic": "langchain-anthropic",
    "langchain_openai": "langchain-openai",
    "langchain_deepseek": "langchain-deepseek"
}

def _build_missing_dependency_hint(module_path, err):
    package = MODULE_TO_PACKAGE_HINTS.get(module_root, module_root)
    return (
        f"Missing dependency '{missing_module}'. "
        f"Install with `uv add {package}` (or `pip install {package}`), "
        "then restart DeerFlow."
    )

Thinking Not Supported

# config.yaml
models:
  - name: gpt-3.5
    supports_thinking: false  # Or omitted

model = create_chat_model(name="gpt-3.5", thinking_enabled=True)
# ValueError: Model gpt-3.5 does not support thinking.
#             Set `supports_thinking: true` in config.yaml

LangSmith Tracing Integration

Factory automatically attaches LangSmith tracer if enabled:

from src.config import is_tracing_enabled, get_tracing_config

if is_tracing_enabled():
    try:
        from langchain_core.tracers.langchain import LangChainTracer
        
        tracing_config = get_tracing_config()
        tracer = LangChainTracer(
            project_name=tracing_config.project
        )
        
        # Attach to model callbacks
        existing_callbacks = model_instance.callbacks or []
        model_instance.callbacks = [*existing_callbacks, tracer]
        
        logger.debug(
            f"LangSmith tracing attached to model '{name}' "
            f"(project='{tracing_config.project}')"
        )
    except Exception as e:
        logger.warning(f"Failed to attach tracing: {e}")

Configuration (config.yaml):

tracing:
  enabled: true
  project: deerflow-production
  # Requires LANGCHAIN_API_KEY environment variable

Custom Model Providers

Adding Custom Providers

Install provider package:
```
uv add langchain-provider-name
```

Add to config.yaml:

models:
  - name: my-custom-model
    display_name: My Custom Model
    use: langchain_provider:ChatProvider
    model: model-id
    api_key: $PROVIDER_API_KEY
    temperature: 0.7

Set environment variables:
```
export PROVIDER_API_KEY=your-key-here
```

Use model:

model = create_chat_model(name="my-custom-model")

Patched Providers

For providers needing workarounds, create patched classes: Example: backend/src/models/patched_deepseek.py

from langchain_deepseek import ChatDeepSeek

class PatchedChatDeepSeek(ChatDeepSeek):
    """Patched DeepSeek client with fixes for specific issues."""
    
    def _generate(self, messages, **kwargs):
        # Apply workarounds here
        # ...
        return super()._generate(messages, **kwargs)

Usage in config:

models:
  - name: deepseek-chat
    use: src.models.patched_deepseek:PatchedChatDeepSeek
    # ...

Usage in Agent System

Lead Agent Creation

def make_lead_agent(config: RunnableConfig):
    # Extract runtime config
    thinking_enabled = config["configurable"].get("thinking_enabled", True)
    reasoning_effort = config["configurable"].get("reasoning_effort")
    model_name = config["configurable"].get("model_name")
    
    # Resolve model (with fallback to default)
    model_name = _resolve_model_name(model_name)
    
    # Create model with runtime settings
    model = create_chat_model(
        name=model_name,
        thinking_enabled=thinking_enabled,
        reasoning_effort=reasoning_effort
    )
    
    # Create agent
    return create_agent(
        model=model,
        tools=get_available_tools(model_name=model_name),
        middleware=_build_middlewares(config, model_name),
        state_schema=ThreadState
    )

Summarization Middleware

def _create_summarization_middleware():
    config = get_summarization_config()
    
    if config.model_name:
        model = config.model_name  # Use specific model name
    else:
        # Use lightweight model for cost savings
        model = create_chat_model(thinking_enabled=False)
    
    return SummarizationMiddleware(model=model, ...)

Title Generation

class TitleMiddleware(AgentMiddleware):
    def _generate_title(self, state):
        # Use lightweight model (no thinking)
        model = create_chat_model(thinking_enabled=False)
        
        response = model.invoke(prompt)
        return response.content.strip()

Testing Models

import pytest
from src.models import create_chat_model

def test_create_default_model():
    model = create_chat_model()
    assert model is not None
    assert hasattr(model, "invoke")

def test_create_with_thinking():
    model = create_chat_model(name="gpt-4o", thinking_enabled=True)
    # Check thinking params were applied
    assert model.extra_body["thinking"]["type"] == "enabled"

def test_vision_support():
    from src.config import get_app_config
    
    config = get_app_config()
    vision_models = [m for m in config.models if m.supports_vision]
    
    assert len(vision_models) > 0
    
    model = create_chat_model(name=vision_models[0].name)
    # Verify ViewImageMiddleware would be added

def test_missing_model_error():
    with pytest.raises(ValueError, match="not found in config"):
        create_chat_model(name="nonexistent-model")

def test_missing_provider_hint():
    # Temporarily remove model from sys.modules
    import sys
    sys.modules.pop("langchain_fake_provider", None)
    
    with pytest.raises(ImportError, match="Install with `uv add"):
        create_chat_model(name="fake-model")

Best Practices

1. Model Selection

# For expensive operations, use cheap model
model = create_chat_model(name="gpt-4o-mini", thinking_enabled=False)

# For complex reasoning, use flagship with thinking
model = create_chat_model(name="gpt-4o", thinking_enabled=True)

# For vision tasks, ensure model supports it
from src.config import get_app_config
config = get_app_config().get_model_config("gpt-4o")
if not config.supports_vision:
    raise ValueError("Vision required but model doesn't support it")

2. Configuration Management

# Separate models for different use cases
models:
  - name: default
    use: langchain_anthropic:ChatAnthropic
    model: claude-3-5-sonnet-20241022
    temperature: 0.7
  
  - name: cheap
    use: langchain_openai:ChatOpenAI
    model: gpt-4o-mini
    temperature: 0.5
  
  - name: vision
    use: langchain_openai:ChatOpenAI
    model: gpt-4o
    supports_vision: true
  
  - name: reasoning
    use: langchain_openai:ChatOpenAI
    model: o1-preview
    supports_reasoning_effort: true

3. Environment Variables

# .env file
OPENAI_API_KEY=sk-...
ANTHROPIC_API_KEY=sk-ant-...
DEEPSEEK_API_KEY=sk-...
DEEPSEEK_BASE_URL=https://api.deepseek.com

4. Error Handling

try:
    model = create_chat_model(name=user_selected_model)
except ValueError as e:
    # Model not found
    logger.error(f"Invalid model selection: {e}")
    model = create_chat_model()  # Fallback to default
except ImportError as e:
    # Provider not installed
    logger.error(f"Model provider missing: {e}")
    raise  # Surface to user with install instructions

Architecture

Development

Troubleshooting

Documentation Index

​Core Function: create_chat_model()

​Model Configuration

​config.yaml Structure

​Field Reference

​Core Fields

​Capability Flags

​Provider Parameters

​when_thinking_enabled

​Reflection-Based Instantiation

​Thinking Mode Support

​Enabling Thinking

​Implementation

​Thinking Configurations

​OpenAI Extended Thinking

​OpenAI o1 Reasoning Effort

​Anthropic Extended Thinking

​Vision Support

​Configuration

​Impact on Agent

​Runtime Parameter Overrides

​Via Keyword Arguments

​Merge Behavior

​Environment Variable Resolution

​Error Handling

​Missing Model

​Missing Provider

​Thinking Not Supported

​LangSmith Tracing Integration

​Custom Model Providers

​Adding Custom Providers

​Patched Providers

​Usage in Agent System

​Lead Agent Creation

​Summarization Middleware

​Title Generation

​Testing Models

​Best Practices

​1. Model Selection

​2. Configuration Management

​3. Environment Variables

​4. Error Handling

​See Also