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Pydantic AI is a Python agent framework built on Pydantic. Braintrust provides native integration to trace Pydantic AI agents, capturing inputs, outputs, tool calls, and performance metrics.

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Setup

Install the Braintrust SDK and Pydantic AI: 
pip install braintrust pydantic-ai

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Trace Pydantic AI agents

Use setup_pydantic_ai() to automatically instrument all Pydantic AI agents and direct API calls: 
from braintrust.wrappers.pydantic_ai import setup_pydantic_ai
from pydantic_ai import Agent

# Initialize Braintrust tracing for Pydantic AI
setup_pydantic_ai(project_name="my-pydantic-project")

# Use agents as normal - they're automatically traced
agent = Agent("openai:gpt-4o", system_prompt="You are a helpful assistant.")
result = await agent.run("What is the capital of France?")
This automatically traces:
  • Agent runs: agent.run(), agent.run_sync(), agent.run_stream(), and agent.run_stream_sync()
  • Direct API calls: model_request(), model_request_sync(), and streaming variants
  • Model interactions: Individual LLM calls made by agents
  • Tool calls: Any tools defined on your agents

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Example with tools and streaming

from braintrust.wrappers.pydantic_ai import setup_pydantic_ai
from pydantic_ai import Agent, ModelSettings

setup_pydantic_ai(project_name="my-pydantic-project")

agent = Agent(
    "openai:gpt-4o",
    model_settings=ModelSettings(max_tokens=500),
)

@agent.tool_plain
def get_weather(city: str) -> str:
    """Get the current weather for a city."""
    return f"22°C and sunny in {city}"

# Streaming is fully traced, including time-to-first-token
async with agent.run_stream("What's the weather in Paris?") as result:
    async for text in result.stream_text(delta=True):
        print(text, end="", flush=True)

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Using with existing spans

If you already have a Braintrust span context (e.g., from @traced or start_span), Pydantic AI traces will nest under it: 
from braintrust import traced
from braintrust.wrappers.pydantic_ai import setup_pydantic_ai
from pydantic_ai import Agent

setup_pydantic_ai(project_name="my-pydantic-project")

agent = Agent("openai:gpt-4o")

@traced
async def my_workflow(question: str):
    # Agent traces appear as children of this span
    result = await agent.run(question)
    return result.output

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Alternative: OpenTelemetry integration

You can also use Braintrust’s OpenTelemetry support with Pydantic AI’s built-in instrumentation: 
from braintrust.otel import BraintrustSpanProcessor
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from pydantic_ai import Agent

provider = TracerProvider()
trace.set_tracer_provider(provider)
provider.add_span_processor(BraintrustSpanProcessor())

Agent.instrument_all()
This requires pip install "braintrust[otel]". See the OpenTelemetry guide for more details.

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