[Reasoning Engine] LangchainAgent.stream_query attempts to import from deprecated langchain.load path

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#6,397 opened on Mar 8, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 55/100

Issue type: Bug
Clarity: Clearly specified
Activity status: Stale
Tech stack: python
Domain: ai, machine-learning

Research direction

Start with query() and stream_query() in the four affected template files: vertexai/agent_engines/templates/langchain.py, langgraph.py, and the corresponding preview/reasoning_engines templates. Compare the imports and run the template tests or reproduce the LangchainAgent and LanggraphAgent calls; done means both methods no longer fail on the deprecated langchain.load import.

Written by the indexing model from the issue text.

Description

api: vertex-ai

Environment details

OS type and version: Ubuntu 24.04.4 LTS
Python version: 3.12.10
pip version: 25.2
google-cloud-aiplatform version: Latest from main

Steps to reproduce

Initialize a LangchainAgent or LanggraphAgent from the agent engine or reasoning engine templates.
Call the query or stream_query method.
Observe that it fails with an ImportError because it attempts to import from langchain.load instead of langchain_core.load.

Code example

from vertexai.agent_engines.templates.langchain import LangchainAgent

# Initialize agent
agent = LangchainAgent(model="gemini-1.5-flash-001")
agent.set_up()

# Both query and stream_query are affected
result = agent.query(input="Hello")

for chunk in agent.stream_query(input="Hello"):
    print(chunk)

Stack trace

Traceback (most recent call last):
  File "example.py", line 8, in <module>
    for chunk in agent.stream_query(input="Hello"):
  File ".../vertexai/agent_engines/templates/langchain.py", line 665, in stream_query
    from langchain.load import dump as langchain_load_dump
ImportError: cannot import name 'dump' from 'langchain.load'

Affected files

The same deprecated import (from langchain.load import dump) exists in both query() and stream_query() across all 4 template modules:

vertexai/agent_engines/templates/langchain.py
vertexai/agent_engines/templates/langgraph.py
vertexai/preview/reasoning_engines/templates/langchain.py
vertexai/preview/reasoning_engines/templates/langgraph.py

Making sure to follow these steps will guarantee the quickest resolution possible.

Thanks!

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