Pydantic AI LLM analytics installation

  1. Install the PostHog SDK

    Required

    Setting up analytics starts with installing the PostHog SDK. The Pydantic AI integration uses PostHog's OpenAI wrapper.

    pip install posthog

  2. Install Pydantic AI

    Required

    Install Pydantic AI with OpenAI support. PostHog instruments your LLM calls by wrapping the OpenAI client that Pydantic AI uses.

    pip install 'pydantic-ai[openai]'

  3. Initialize PostHog and Pydantic AI

    Required

    Initialize PostHog with your project API key and host from your project settings, then create a PostHog AsyncOpenAI wrapper, pass it to an OpenAIProvider, and use that with Pydantic AI's OpenAIChatModel.

    from pydantic_ai import Agent
    from pydantic_ai.models.openai import OpenAIChatModel
    from pydantic_ai.providers.openai import OpenAIProvider
    from posthog.ai.openai import AsyncOpenAI
    from posthog import Posthog
    

    posthog = Posthog(
        "<ph_project_api_key>",
        host="https://us.i.posthog.com"
    )
    

    openai_client = AsyncOpenAI(
        api_key="your_openai_api_key",
        posthog_client=posthog
    )
    

    provider = OpenAIProvider(openai_client=openai_client)
    

    model = OpenAIChatModel(
        "gpt-4o-mini",
        provider=provider
    )
    How this works

    PostHog's AsyncOpenAI wrapper is a proper subclass of openai.AsyncOpenAI, so it works directly as the client for Pydantic AI's OpenAIProvider. PostHog captures $ai_generation events automatically without proxying your calls.

  4. Run your agent

    Required

    Create a Pydantic AI agent with the model and run it. PostHog automatically captures an $ai_generation event for each LLM call.

    agent = Agent(
        model,
        system_prompt="You are a helpful assistant.",
    )
    

    result = agent.run_sync(
        "Tell me a fun fact about hedgehogs.",
        # Pass PostHog metadata via the OpenAI client's extra params
    )
    

    print(result.output)

    You can expect captured $ai_generation events to have the following properties:

    PropertyDescription
    $ai_modelThe specific model, like gpt-5-mini or claude-4-sonnet
    $ai_latencyThe latency of the LLM call in seconds
    $ai_time_to_first_tokenTime to first token in seconds (streaming only)
    $ai_toolsTools and functions available to the LLM
    $ai_inputList of messages sent to the LLM
    $ai_input_tokensThe number of tokens in the input (often found in response.usage)
    $ai_output_choicesList of response choices from the LLM
    $ai_output_tokensThe number of tokens in the output (often found in response.usage)
    $ai_total_cost_usdThe total cost in USD (input + output)
    [...]See full list of properties

  5. Verify traces and generations

    Recommended
    Confirm LLM events are being sent to PostHog

    Let's make sure LLM events are being captured and sent to PostHog. Under LLM analytics, you should see rows of data appear in the Traces and Generations tabs.


    LLM generations in PostHog
    Check for LLM events in PostHog

  6. Next steps

    Recommended

    Now that you're capturing AI conversations, continue with the resources below to learn what else LLM Analytics enables within the PostHog platform.

    ResourceDescription
    BasicsLearn the basics of how LLM calls become events in PostHog.
    GenerationsRead about the $ai_generation event and its properties.
    TracesExplore the trace hierarchy and how to use it to debug LLM calls.
    SpansReview spans and their role in representing individual operations.
    Anaylze LLM performanceLearn how to create dashboards to analyze LLM performance.

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