diff --git a/packages/api/src/microsoft_teams/api/activities/conversation/conversation_update.py b/packages/api/src/microsoft_teams/api/activities/conversation/conversation_update.py
index c13aa338..971020e1 100644
--- a/packages/api/src/microsoft_teams/api/activities/conversation/conversation_update.py
+++ b/packages/api/src/microsoft_teams/api/activities/conversation/conversation_update.py
@@ -3,7 +3,9 @@
 Licensed under the MIT License.
 """
 
-from typing import List, Literal, Optional
+from typing import Any, List, Literal, Optional
+
+from pydantic import model_validator
 
 from ...models import Account, ActivityBase, ActivityInputBase, ChannelData, CustomBaseModel
 
@@ -49,10 +51,51 @@ class _ConversationUpdateBase(CustomBaseModel):
 
 
 class ConversationUpdateActivity(_ConversationUpdateBase, ActivityBase):
-    """Output model for received conversation update activities with required fields and read-only properties."""
+    """Output model for received conversation update activities with required fields and read-only properties.
+
+    Design note (channel_data field):
+        In Teams, conversationUpdate activities always include channelData with an eventType
+        discriminator (e.g. "channelCreated", "teamArchived"). The routing system
+        (activity_route_configs.py) relies on channel_data.event_type to dispatch to specific
+        handlers like on_channel_created() and on_team_archived().
+
+        However, non-Teams channels (notably Direct Line) send conversationUpdate activities
+        WITHOUT channelData, which would cause a Pydantic ValidationError if the field were
+        strictly required. See https://github.com/microsoft/teams.py/issues/239.
+
+        Resolution: We keep channel_data as a REQUIRED field (preserving the type contract for
+        the 99% of developers building Teams bots) but add a model_validator that defaults it to
+        an empty ConversationChannelData() when missing from the incoming payload. This matches
+        the TypeScript SDK pattern, where the type declares channelData as required on
+        IConversationUpdateActivity (conversation-update.ts:25) but the router uses optional
+        chaining defensively (router.ts:73-87).
+
+        The empty default means:
+        - Teams activities: channel_data is populated normally, event_type routes work as before
+        - Direct Line activities: channel_data is an empty ConversationChannelData (event_type=None),
+          so Teams-specific event handlers don't fire, but the generic on_conversation_update()
+          handler still does
+        - Type checkers see a non-optional ConversationChannelData — no None-guards needed
+    """
 
     channel_data: ConversationChannelData  # pyright: ignore [reportGeneralTypeIssues, reportIncompatibleVariableOverride]
-    """Channel data with event type information."""
+    """Channel data with event type information. Always present — defaulted to empty for non-Teams channels."""
+
+    @model_validator(mode="before")
+    @classmethod
+    def _default_channel_data(cls, data: Any) -> Any:
+        """Supply an empty channelData when absent (e.g. Direct Line).
+
+        Without this, Pydantic rejects the payload because channel_data is required.
+        The empty default preserves the required-field contract for Teams developers
+        while allowing non-Teams channels to send conversationUpdate without channelData.
+        See: https://github.com/microsoft/teams.py/issues/239
+        """
+        if isinstance(data, dict):
+            # Check both the snake_case field name and the camelCase alias
+            if "channel_data" not in data and "channelData" not in data:
+                data["channelData"] = {}
+        return data
 
 
 class ConversationUpdateActivityInput(_ConversationUpdateBase, ActivityInputBase):