diff --git a/python/test_client.py b/python/test_client.py
index 62ae7b188..e2e08d3f5 100644
--- a/python/test_client.py
+++ b/python/test_client.py
@@ -480,3 +480,26 @@ async def mock_request(method, params):
             assert captured["session.model.switchTo"]["modelId"] == "gpt-4.1"
         finally:
             await client.force_stop()
+
+    @pytest.mark.asyncio
+    async def test_list_sessions_sends_empty_payload_without_filter(self):
+        client = CopilotClient({"cli_path": CLI_PATH})
+        await client.start()
+
+        try:
+            captured = {}
+            original_request = client._client.request
+
+            async def mock_request(method, params):
+                captured[method] = params
+                if method == "session.list":
+                    return {"sessions": []}
+                return await original_request(method, params)
+
+            client._client.request = mock_request
+            sessions = await client.list_sessions()
+
+            assert captured["session.list"] == {}
+            assert sessions == []
+        finally:
+            await client.force_stop()