diff --git a/src/xpk/core/system_characteristics.py b/src/xpk/core/system_characteristics.py
index 400dc632a..4d3e5aa72 100644
--- a/src/xpk/core/system_characteristics.py
+++ b/src/xpk/core/system_characteristics.py
@@ -166,12 +166,16 @@ def get_tpu_system_characteristics_map(
     supported_topologies: list[str],
     supports_sub_slicing: bool,
     tpu_type_requires_workload_policy: bool = False,
+    default_topologies: set[str] | None = None,
 ) -> dict[str, SystemCharacteristics]:
   system_characteristics_map = {}
+  if default_topologies is None:
+    default_topologies = set()
   for topology in supported_topologies:
     chips_per_vm = compute_chips_per_vm(topology)
     vms_per_slice = compute_vms_per_slice(topology)
     num_tensorcores = compute_num_tensorcores(tensorcores_per_chip, topology)
+    device_type = f'{prefix}-{num_tensorcores}'
     system = SystemCharacteristics(
         topology=topology,
         vms_per_slice=vms_per_slice,
@@ -179,13 +183,17 @@ def get_tpu_system_characteristics_map(
         gce_machine_type=machine_type,
         chips_per_vm=chips_per_vm,
         accelerator_type=AcceleratorType.TPU,
-        device_type=f'{prefix}-{num_tensorcores}',
+        device_type=device_type,
         requires_workload_policy=tpu_type_requires_workload_policy
         and vms_per_slice > 1,
         supports_sub_slicing=supports_sub_slicing,
     )
     system_characteristics_map[f'{prefix}-{topology}'] = system
-    system_characteristics_map[f'{prefix}-{num_tensorcores}'] = system
+    if (
+        topology in default_topologies
+        or device_type not in system_characteristics_map
+    ):
+      system_characteristics_map[device_type] = system
 
   return system_characteristics_map
 
@@ -373,6 +381,106 @@ def compute_vms_per_slice(topology: str) -> int:
         tpu_type_requires_workload_policy=True,
         supports_sub_slicing=False,
         supported_topologies=generate_tpu_topologies(max_cubes=144),
+        default_topologies=set([
+            '12x12x12',
+            '12x12x16',
+            '12x12x20',
+            '12x12x24',
+            '12x12x28',
+            '12x12x36',
+            '12x16x16',
+            '12x16x20',
+            '12x16x24',
+            '12x16x28',
+            '12x20x20',
+            '12x20x24',
+            '12x24x24',
+            '16x16x16',
+            '16x16x20',
+            '16x16x24',
+            '16x16x32',
+            '16x20x28',
+            '16x24x24',
+            '2x2x1',
+            '2x2x2',
+            '2x2x4',
+            '2x4x4',
+            '4x12x116',
+            '4x12x12',
+            '4x12x124',
+            '4x12x20',
+            '4x12x28',
+            '4x12x44',
+            '4x12x52',
+            '4x12x68',
+            '4x12x76',
+            '4x12x92',
+            '4x20x20',
+            '4x20x28',
+            '4x20x44',
+            '4x20x52',
+            '4x20x68',
+            '4x20x76',
+            '4x28x28',
+            '4x28x44',
+            '4x28x52',
+            '4x4x116',
+            '4x4x12',
+            '4x4x124',
+            '4x4x148',
+            '4x4x164',
+            '4x4x172',
+            '4x4x188',
+            '4x4x20',
+            '4x4x212',
+            '4x4x236',
+            '4x4x244',
+            '4x4x28',
+            '4x4x4',
+            '4x4x44',
+            '4x4x52',
+            '4x4x68',
+            '4x4x76',
+            '4x4x8',
+            '4x4x92',
+            '4x8x116',
+            '4x8x12',
+            '4x8x124',
+            '4x8x148',
+            '4x8x164',
+            '4x8x172',
+            '4x8x188',
+            '4x8x20',
+            '4x8x28',
+            '4x8x44',
+            '4x8x52',
+            '4x8x68',
+            '4x8x76',
+            '4x8x8',
+            '4x8x92',
+            '8x12x12',
+            '8x12x16',
+            '8x12x20',
+            '8x12x28',
+            '8x12x44',
+            '8x12x52',
+            '8x16x16',
+            '8x16x20',
+            '8x16x28',
+            '8x16x44',
+            '8x20x20',
+            '8x20x28',
+            '8x8x12',
+            '8x8x16',
+            '8x8x20',
+            '8x8x28',
+            '8x8x44',
+            '8x8x52',
+            '8x8x68',
+            '8x8x76',
+            '8x8x8',
+            '8x8x92',
+        ]),
     ),
     **get_tpu_system_characteristics_map(
         prefix='v6e',
@@ -405,6 +513,104 @@ def compute_vms_per_slice(topology: str) -> int:
         machine_type='ct5p-hightpu-4t',
         supports_sub_slicing=False,
         supported_topologies=generate_tpu_topologies(max_cubes=140),
+        default_topologies=set([
+            '2x2x1',
+            '2x2x2',
+            '2x2x4',
+            '2x4x4',
+            '4x4x4',
+            '4x4x8',
+            '4x4x12',
+            '4x8x8',
+            '4x4x20',
+            '4x8x12',
+            '4x4x28',
+            '8x8x8',
+            '4x12x12',
+            '4x8x20',
+            '4x4x44',
+            '8x8x12',
+            '4x4x52',
+            '4x8x28',
+            '4x12x20',
+            '8x8x16',
+            '4x4x68',
+            '8x12x12',
+            '4x4x76',
+            '8x8x20',
+            '4x12x28',
+            '4x8x44',
+            '4x4x92',
+            '8x12x16',
+            '4x20x20',
+            '4x8x52',
+            '12x12x12',
+            '8x8x28',
+            '4x4x116',
+            '8x12x20',
+            '4x4x124',
+            '8x16x16',
+            '4x12x44',
+            '4x8x68',
+            '4x20x28',
+            '12x12x16',
+            '4x4x148',
+            '4x8x76',
+            '4x12x52',
+            '8x16x20',
+            '4x4x164',
+            '8x12x28',
+            '4x4x172',
+            '8x8x44',
+            '12x12x20',
+            '4x8x92',
+            '4x4x188',
+            '12x16x16',
+            '4x28x28',
+            '8x20x20',
+            '4x12x68',
+            '8x8x52',
+            '4x4x212',
+            '12x12x24',
+            '4x20x44',
+            '8x16x28',
+            '4x12x76',
+            '4x8x116',
+            '4x4x236',
+            '12x16x20',
+            '4x4x244',
+            '4x8x124',
+            '12x12x28',
+            '16x16x16',
+            '4x20x52',
+            '8x12x44',
+            '8x8x68',
+            '4x12x92',
+            '8x20x28',
+            '12x16x24',
+            '4x8x148',
+            '12x20x20',
+            '8x8x76',
+            '4x28x44',
+            '8x12x52',
+            '16x16x20',
+            '12x12x36',
+            '4x8x164',
+            '12x16x28',
+            '4x20x68',
+            '4x8x172',
+            '4x12x116',
+            '8x16x44',
+            '12x20x24',
+            '4x28x52',
+            '8x8x92',
+            '4x12x124',
+            '4x8x188',
+            '4x20x76',
+            '16x16x24',
+            '12x24x24',
+            '16x20x28',
+        ]),
     ),
     **get_tpu_system_characteristics_map(
         prefix='v5litepod',
@@ -423,6 +629,19 @@ def compute_vms_per_slice(topology: str) -> int:
         supported_topologies=generate_tpu_topologies(
             max_cubes=64, enforce_nondecreasing=False
         ),
+        default_topologies=set([
+            '2x2x1',
+            '2x2x2',
+            '2x2x4',
+            '2x4x4',
+            '4x4x4',
+            '4x4x8',
+            '4x8x8',
+            '8x8x8',
+            '8x8x12',
+            '8x8x16',
+            '8x16x16',
+        ]),
     ),
     # CPU system characteristics.
     # Note that chips_per_vm is actually the number of vCPUs in that CPU.
diff --git a/src/xpk/core/system_characteristics_test.py b/src/xpk/core/system_characteristics_test.py
index 981bf28ba..befe283d1 100644
--- a/src/xpk/core/system_characteristics_test.py
+++ b/src/xpk/core/system_characteristics_test.py
@@ -101,6 +101,21 @@ def test_get_tpu_system_characteristics_map_returns_correct_values_for_2x2x2_top
   }
 
 
+def test_get_tpu_system_characteristics_map_prefers_default_topologies():
+  result = get_tpu_system_characteristics_map(
+      prefix="test",
+      tensorcores_per_chip=2,
+      gke_accelerator="test",
+      machine_type="test",
+      supported_topologies=["4x4x4", "4x4x32", "4x8x16", "8x8x8"],
+      supports_sub_slicing=False,
+      default_topologies=set(["4x8x16"]),
+  )
+
+  assert result["test-128"].topology == "4x4x4"
+  assert result["test-1024"].topology == "4x8x16"
+
+
 def test_generate_tpu_topologies_returns_correct_number_of_values_for_TPU_platforms():
   v4 = generate_tpu_topologies(max_cubes=64, enforce_nondecreasing=False)
   v5p = generate_tpu_topologies(max_cubes=140)