From b4cc730f76d85af09e6132d304bbaa3e8f764e34 Mon Sep 17 00:00:00 2001
From: Spectual <spectual@icloud.com>
Date: Fri, 3 Apr 2026 13:58:04 -0700
Subject: [PATCH] fix(langchain): pass trace_name to propagate_attributes() in
 on_chain_start

When a LangChain chain starts at the root level, `on_chain_start` was not
passing `trace_name` to `propagate_attributes()`, so the trace name was not
being set correctly for the resulting trace.

Fixes #1602
---
 langfuse/langchain/CallbackHandler.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index 8d2c8db90..2c06a6ddf 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -369,6 +369,7 @@ def on_chain_start(
                     session_id=parsed_trace_attributes.get("session_id", None),
                     tags=parsed_trace_attributes.get("tags", None),
                     metadata=parsed_trace_attributes.get("metadata", None),
+                    trace_name=span_name,
                 )
 
                 self._propagation_context_manager.__enter__()