Fix topo sort for listed deps

airflow-core/src/airflow/serialization/definitions/taskgroup.py

@@ -243,8 +243,16 @@ def topological_sort(self) -> list[DAGNode]:
                         # We are already going to visit that TG
                         break
                 else:
-                    del graph_unsorted[node.node_id]
-                    graph_sorted.append(node)
+                    # When list-based deps (e.g. `[b0, b1] >> a`) are used between TaskGroups,
+                    # only upstream_group_ids is populated (not upstream_task_ids), so upstream_list
+                    # is empty and the task-level check above won't block the node. Check group-level
+                    # upstreams explicitly to handle this case.
+                    for group_id in getattr(node, "upstream_group_ids", ()):
+                        if group_id in graph_unsorted:
+                            break
+                    else:
+                        del graph_unsorted[node.node_id]
+                        graph_sorted.append(node)
         return graph_sorted
 
     def add(self, node: DAGNode) -> DAGNode:

airflow-core/tests/unit/utils/test_task_group.py

@@ -1117,6 +1117,28 @@ def nested_topo(group):
     ]
 
 
+def test_topological_group_dep_list_syntax():
+    """List-based deps (`[b0, b1] >> a`) must produce the same topological order as individual deps."""
+    logical_date = pendulum.parse("20200101")
+    with DAG("test_dag_list_dep", schedule=None, start_date=logical_date) as dag:
+        with TaskGroup("a") as tg_a:
+            EmptyOperator(task_id="task")
+
+        groups = []
+        for x in range(3):
+            with TaskGroup(f"b_{x}") as tg_b:
+                EmptyOperator(task_id="task")
+            groups.append(tg_b)
+
+        groups >> tg_a  # list-based dep — previously produced wrong order
+
+    top_level = dag.task_group.topological_sort()
+    ids = [node.node_id for node in top_level]
+    a_idx = ids.index("a")
+    b_idxs = [ids.index(f"b_{x}") for x in range(3)]
+    assert all(b < a_idx for b in b_idxs), f"Expected all b_x before a in topological order, got: {ids}"
+
+
 def test_task_group_arrow_with_setup_group():
     with DAG(dag_id="setup_group_teardown_group") as dag:
         with TaskGroup("group_1") as g1:

task-sdk/src/airflow/sdk/definitions/taskgroup.py

@@ -559,9 +559,17 @@ def topological_sort(self):
                         # We are already going to visit that TG
                         break
                 else:
-                    acyclic = True
-                    del graph_unsorted[node.node_id]
-                    graph_sorted.append(node)
+                    # When list-based deps (e.g. `[b0, b1] >> a`) are used between TaskGroups,
+                    # only upstream_group_ids is populated (not upstream_task_ids), so upstream_list
+                    # is empty and the task-level check above won't block the node. Check group-level
+                    # upstreams explicitly to handle this case.
+                    for group_id in getattr(node, "upstream_group_ids", ()):
+                        if group_id in graph_unsorted:
+                            break
+                    else:
+                        acyclic = True
+                        del graph_unsorted[node.node_id]
+                        graph_sorted.append(node)
 
             if not acyclic:
                 raise AirflowDagCycleException(f"A cyclic dependency occurred in dag: {self.dag_id}")