From 79e7feccb8c57b822d65b7f43d634b9a53863e1d Mon Sep 17 00:00:00 2001
From: Hassieb Pakzad <68423100+hassiebp@users.noreply.github.com>
Date: Tue, 19 Aug 2025 14:47:06 +0200
Subject: [PATCH 1/3] feat(langchain): add update_trace argument

---
 langfuse/langchain/CallbackHandler.py | 30 +++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index 7c898807c..8d6dfb126 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -56,7 +56,9 @@
 
 
 class LangchainCallbackHandler(LangchainBaseCallbackHandler):
-    def __init__(self, *, public_key: Optional[str] = None) -> None:
+    def __init__(
+        self, *, public_key: Optional[str] = None, update_trace: Optional[bool] = False
+    ) -> None:
         self.client = get_client(public_key=public_key)
 
         self.runs: Dict[UUID, Union[LangfuseSpan, LangfuseGeneration]] = {}
@@ -64,6 +66,7 @@ def __init__(self, *, public_key: Optional[str] = None) -> None:
         self.updated_completion_start_time_memo: Set[UUID] = set()
 
         self.last_trace_id: Optional[str] = None
+        self.update_trace = update_trace
 
     def on_llm_new_token(
         self,
@@ -207,7 +210,19 @@ def on_chain_start(
                     ),
                 )
                 span.update_trace(
-                    **self._parse_langfuse_trace_attributes_from_metadata(metadata)
+                    **(
+                        cast(
+                            Any,
+                            {
+                                "input": inputs,
+                                "name": span_name,
+                                "metadata": span_metadata,
+                            },
+                        )
+                        if self.update_trace
+                        else {}
+                    ),
+                    **self._parse_langfuse_trace_attributes_from_metadata(metadata),
                 )
                 self.runs[run_id] = span
             else:
@@ -322,14 +337,21 @@ def on_chain_end(
             if run_id not in self.runs:
                 raise Exception("run not found")
 
-            self.runs[run_id].update(
+            span = self.runs[run_id]
+            span.update(
                 output=outputs,
                 input=kwargs.get("inputs"),
-            ).end()
+            )
+
+            if parent_run_id is None and self.update_trace:
+                span.update_trace(output=outputs, input=kwargs.get("inputs"))
+
+            span.end()
 
             del self.runs[run_id]
 
             self._deregister_langfuse_prompt(run_id)
+
         except Exception as e:
             langfuse_logger.exception(e)
 

From f7b064b38a9a4f0566db57fd1627959a8cd61451 Mon Sep 17 00:00:00 2001
From: Hassieb Pakzad <68423100+hassiebp@users.noreply.github.com>
Date: Tue, 19 Aug 2025 14:52:07 +0200
Subject: [PATCH 2/3] Update langfuse/langchain/CallbackHandler.py

Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>
---
 langfuse/langchain/CallbackHandler.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index 8d6dfb126..5de36966b 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -57,7 +57,7 @@
 
 class LangchainCallbackHandler(LangchainBaseCallbackHandler):
     def __init__(
-        self, *, public_key: Optional[str] = None, update_trace: Optional[bool] = False
+        self, *, public_key: Optional[str] = None, update_trace: bool = False
     ) -> None:
         self.client = get_client(public_key=public_key)
 

From e96f13b77ee42ee2d078617395621be0e7affdf4 Mon Sep 17 00:00:00 2001
From: Hassieb Pakzad <68423100+hassiebp@users.noreply.github.com>
Date: Tue, 19 Aug 2025 14:50:14 +0200
Subject: [PATCH 3/3] add docs

---
 langfuse/langchain/CallbackHandler.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index 5de36966b..ba2460c47 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -59,6 +59,12 @@ class LangchainCallbackHandler(LangchainBaseCallbackHandler):
     def __init__(
         self, *, public_key: Optional[str] = None, update_trace: bool = False
     ) -> None:
+        """Initialize the LangchainCallbackHandler.
+
+        Args:
+            public_key: Optional Langfuse public key. If not provided, will use the default client configuration.
+            update_trace: Whether to update the Langfuse trace with the chains input / output / metadata / name. Defaults to False.
+        """
         self.client = get_client(public_key=public_key)
 
         self.runs: Dict[UUID, Union[LangfuseSpan, LangfuseGeneration]] = {}