diff --git a/api/agent.py b/api/agent.py
index dde8ca5..8e2e984 100644
--- a/api/agent.py
+++ b/api/agent.py
@@ -23,7 +23,14 @@ import logging
 from typing import Any, TypedDict
 
 from langgraph.graph import END, StateGraph
-from openai import AzureOpenAI
+# Drop-in for `openai.AzureOpenAI` - identical constructor and call signatures,
+# and it records every call to Langfuse as a generation carrying the model and
+# the token usage the plain client discards. That is the only thing Langfuse
+# can price, so this import is what makes cost appear in the UI. Reads
+# LANGFUSE_PUBLIC_KEY / LANGFUSE_SECRET_KEY / LANGFUSE_HOST from the
+# environment, which the api service already has. Falls back to plain
+# behaviour when they are unset - observability never breaks the answer path.
+from langfuse.openai import AzureOpenAI
 
 import classifier
 import tools.equipment as equipment_tool