diff --git a/nanobot/channels/feishu.py b/nanobot/channels/feishu.py
index d5943f9a0..e709c4a2d 100644
--- a/nanobot/channels/feishu.py
+++ b/nanobot/channels/feishu.py
@@ -258,6 +258,7 @@ class FeishuConfig(Base):
     reply_to_message: bool = False  # If True, bot replies quote the user's original message
     streaming: bool = True
     domain: Literal["feishu", "lark"] = "feishu"  # Set to "lark" for international Lark
+    topic_isolation: bool = True  # If True, each topic in group chat gets its own session (isolation)
 
 
 _STREAM_ELEMENT_ID = "streaming_md"
@@ -1770,12 +1771,15 @@ class FeishuChannel(BaseChannel):
             if not content and not media_paths:
                 return
 
-            # Build topic-scoped session key for conversation isolation.
-            # Group chat: each topic gets its own session via root_id (replies
-            # inside a topic) or message_id (top-level messages start a new topic).
+            # Build session key for conversation isolation.
+            # If topic_isolation is True: each topic gets its own session via root_id/message_id.
+            # If topic_isolation is False: all messages in group share the same session.
             # Private chat: no override — same behavior as Telegram/Slack.
             if chat_type == "group":
-                session_key = f"feishu:{chat_id}:{root_id or message_id}"
+                if self.config.topic_isolation:
+                    session_key = f"feishu:{chat_id}:{root_id or message_id}"
+                else:
+                    session_key = f"feishu:{chat_id}"
             else:
                 session_key = None
 
diff --git a/tests/channels/test_feishu_reply.py b/tests/channels/test_feishu_reply.py
index b43a177d1..7be3fff65 100644
--- a/tests/channels/test_feishu_reply.py
+++ b/tests/channels/test_feishu_reply.py
@@ -912,3 +912,95 @@ async def test_on_message_ignores_unauthorized_sender_before_side_effects() -> N
     channel._download_and_save_media.assert_not_awaited()
     channel.transcribe_audio.assert_not_awaited()
     channel._handle_message.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_session_key_with_topic_isolation_true_uses_thread_scoped() -> None:
+    """When topic_isolation is True (default), group messages use thread-scoped session keys."""
+    channel = _make_feishu_channel(group_policy="open")
+    channel.config.topic_isolation = True
+    bus_spy = []
+    original_publish = channel.bus.publish_inbound
+
+    async def capture(msg):
+        bus_spy.append(msg)
+        await original_publish(msg)
+
+    channel.bus.publish_inbound = capture
+    channel._download_and_save_media = AsyncMock(return_value=(None, ""))
+    channel.transcribe_audio = AsyncMock(return_value="")
+    channel._add_reaction = AsyncMock(return_value=None)
+
+    # Test with root_id
+    event1 = _make_feishu_event(
+        chat_type="group",
+        content='{"text": "hello"}',
+        root_id="om_root123",
+        message_id="om_child456",
+    )
+    await channel._on_message(event1)
+
+    # Test without root_id
+    event2 = _make_feishu_event(
+        chat_type="group",
+        content='{"text": "another"}',
+        root_id=None,
+        message_id="om_001",
+    )
+    await channel._on_message(event2)
+
+    assert len(bus_spy) == 2
+    assert bus_spy[0].session_key_override == "feishu:oc_abc:om_root123"
+    assert bus_spy[1].session_key_override == "feishu:oc_abc:om_001"
+
+
+@pytest.mark.asyncio
+async def test_session_key_with_topic_isolation_false_uses_group_scoped() -> None:
+    """When topic_isolation is False, all group messages share the same session key (no isolation)."""
+    channel = _make_feishu_channel(group_policy="open")
+    channel.config.topic_isolation = False
+    bus_spy = []
+    original_publish = channel.bus.publish_inbound
+
+    async def capture(msg):
+        bus_spy.append(msg)
+        await original_publish(msg)
+
+    channel.bus.publish_inbound = capture
+    channel._download_and_save_media = AsyncMock(return_value=(None, ""))
+    channel.transcribe_audio = AsyncMock(return_value="")
+    channel._add_reaction = AsyncMock(return_value=None)
+
+    # Test with root_id
+    event1 = _make_feishu_event(
+        chat_type="group",
+        content='{"text": "hello"}',
+        root_id="om_root123",
+        message_id="om_child456",
+    )
+    await channel._on_message(event1)
+
+    # Test without root_id
+    event2 = _make_feishu_event(
+        chat_type="group",
+        content='{"text": "another"}',
+        root_id=None,
+        message_id="om_001",
+    )
+    await channel._on_message(event2)
+
+    # Private chat still works
+    event3 = _make_feishu_event(
+        chat_type="p2p",
+        content='{"text": "private"}',
+        root_id=None,
+        message_id="om_private",
+    )
+    await channel._on_message(event3)
+
+    assert len(bus_spy) == 3
+    # Group messages all share the same key
+    assert bus_spy[0].session_key_override == "feishu:oc_abc"
+    assert bus_spy[1].session_key_override == "feishu:oc_abc"
+    # Private chat has no session key override
+    assert bus_spy[2].session_key_override is None