fix(llma): LangChain 1.0+ compatibility for CallbackHandler (#363)

* fix: Add LangChain 1.0+ compatibility for CallbackHandler imports

- Use try/except to import from langchain_core first (LangChain 1.0+)
- Fall back to legacy langchain imports for older versions
- Maintains backward compatibility with LangChain 0.x
- All existing tests pass (45 passed)

Fixes #362

* test: Add regression test for AgentAction/AgentFinish imports

- Tests that AgentAction and AgentFinish can be imported
- Tests on_agent_action and on_agent_finish callbacks with mock data
- Ensures compatibility with both LangChain 0.x and 1.0+
- Catches the import issue that was previously only tested with API keys

This addresses a test coverage gap identified during code review.

* chore: Add CHANGELOG entry for LangChain 1.0+ compatibility fix

* fix: Remove unused type: ignore comments for mypy

The type: ignore comments were only needed when the except block
executes, but CI runs with LangChain 1.0+ so the try block succeeds.
Mypy flags these as unused-ignore errors.

* chore: bump version to 6.7.12 for langchain 1.0 compatibility

CHANGELOG.md

@@ -1,6 +1,7 @@
-# Unreleased
+# 6.7.12 - 2025-11-02
 
 - fix(django): Restore process_exception method to capture view and downstream middleware exceptions (fixes #329)
+- fix(ai/langchain): Add LangChain 1.0+ compatibility for CallbackHandler imports (fixes #362)
 
 # 6.7.11 - 2025-10-28
 

posthog/ai/langchain/callbacks.py

@@ -20,8 +20,14 @@ from typing import (
 )
 from uuid import UUID
 
-from langchain.callbacks.base import BaseCallbackHandler
-from langchain.schema.agent import AgentAction, AgentFinish
+try:
+    # LangChain 1.0+ and modern 0.x with langchain-core
+    from langchain_core.callbacks.base import BaseCallbackHandler
+    from langchain_core.agents import AgentAction, AgentFinish
+except (ImportError, ModuleNotFoundError):
+    # Fallback for older LangChain versions
+    from langchain.callbacks.base import BaseCallbackHandler
+    from langchain.schema.agent import AgentAction, AgentFinish
 from langchain_core.documents import Document
 from langchain_core.messages import (
     AIMessage,

posthog/test/ai/langchain/test_callbacks.py

@@ -1877,3 +1877,46 @@ def test_tool_definition(mock_client):
     assert props["$ai_latency"] == 1.0
     # Verify that tools are captured in the $ai_tools property
     assert props["$ai_tools"] == tools
+
+
+def test_agent_action_and_finish_imports():
+    """
+    Regression test for LangChain 1.0+ compatibility (Issue #362).
+    Verifies that AgentAction and AgentFinish can be imported and used.
+    This test ensures the imports work with both LangChain 0.x and 1.0+.
+    """
+    # Import the types that caused the compatibility issue
+    try:
+        from langchain_core.agents import AgentAction, AgentFinish
+    except (ImportError, ModuleNotFoundError):
+        from langchain.schema.agent import AgentAction, AgentFinish  # type: ignore
+
+    # Verify they're available in the callbacks module
+    from posthog.ai.langchain.callbacks import CallbackHandler
+
+    # Test on_agent_action with mock data
+    mock_client = MagicMock()
+    callbacks = CallbackHandler(mock_client)
+    run_id = uuid.uuid4()
+    parent_run_id = uuid.uuid4()
+
+    # Create mock AgentAction
+    action = AgentAction(tool="test_tool", tool_input="test_input", log="test_log")
+
+    # Should not raise an exception
+    callbacks.on_agent_action(action, run_id=run_id, parent_run_id=parent_run_id)
+
+    # Verify parent was set
+    assert run_id in callbacks._parent_tree
+    assert callbacks._parent_tree[run_id] == parent_run_id
+
+    # Test on_agent_finish with mock data
+    finish = AgentFinish(return_values={"output": "test_output"}, log="finish_log")
+
+    # Should not raise an exception
+    callbacks.on_agent_finish(finish, run_id=run_id, parent_run_id=parent_run_id)
+
+    # Verify capture was called
+    assert mock_client.capture.call_count == 1
+    call_args = mock_client.capture.call_args[1]
+    assert call_args["event"] == "$ai_span"

posthog/version.py

@@ -1,4 +1,4 @@
-VERSION = "6.7.11"
+VERSION = "6.7.12"
 
 if __name__ == "__main__":
     print(VERSION, end="")  # noqa: T201