LlamaIndex

2

Install LlamaIndex

Required

Install LlamaIndex with the OpenAI integration. PostHog instruments your LLM calls by wrapping the OpenAI client that LlamaIndex uses.

pip install llama-index llama-index-llms-openai

3

Initialize PostHog and LlamaIndex

Required

Initialize PostHog with your project token and host from your project settings (opens in a new tab), then create a PostHog OpenAI wrapper and pass it to LlamaIndex’s OpenAI LLM class.

from llama_index.llms.openai import OpenAI as LlamaOpenAI
from posthog.ai.openai import OpenAI
from posthog import Posthog
posthog = Posthog(
    "<ph_project_token>",
    host="https://us.i.posthog.com"
)
openai_client = OpenAI(
    api_key="your_openai_api_key",
    posthog_client=posthog
)
llm = LlamaOpenAI(
    model="gpt-5-mini",
    api_key="your_openai_api_key",
)
llm._client = openai_client

How this works

PostHog’s OpenAI wrapper is a proper subclass of openai.OpenAI, so it can replace the internal client used by LlamaIndex’s OpenAI LLM. PostHog captures $ai_generation events automatically without proxying your calls. Note: This approach accesses an internal attribute (_client) which may change in future LlamaIndex versions. Check for updates if you encounter issues after upgrading LlamaIndex.

4

Query with LlamaIndex

Required

Use LlamaIndex as normal. PostHog automatically captures an $ai_generation event for each LLM call made through the wrapped client.

from llama_index.core import VectorStoreIndex, SimpleDirectoryReader
# Load your documents
documents = SimpleDirectoryReader("data").load_data()
# Create an index
index = VectorStoreIndex.from_documents(documents, llm=llm)
# Query the index
query_engine = index.as_query_engine(llm=llm)
response = query_engine.query("What is this document about?")
print(response)

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

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.

Check for LLM events in PostHog (opens in a new tab)

5

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.