diff --git a/.github/workflows/ci-macos.yml b/.github/workflows/ci-macos.yml
index fe9bfa898d5e..224f9b90ae83 100644
--- a/.github/workflows/ci-macos.yml
+++ b/.github/workflows/ci-macos.yml
@@ -56,9 +56,18 @@ on:
         required: false
         default: ""
         type: string
+      # "layered" also uploads the product as four layer artifacts plus an
+      # index, and consumers try those before the aggregate. Off by default:
+      # measured 2026-09-27 on the owned minis, the layer uploads added 100 to
+      # 255 s to compile admission (which every shard waits on), and a shard's
+      # layer restore took 68 to 231 s (median about 115 s) against 34 to 90 s
+      # (median about 70 s) for the aggregate over parallel range requests.
+      # No caller passes this input today; a canary passes
+      # `product_artifacts: layered` from ci.yml's macos call
+      # (docs/ci/app-host-layer-transport.md).
       product_artifacts:
         required: false
-        default: "layered"
+        default: "aggregate"
         type: string
       compile_admitted:
         required: true
diff --git a/tests/test_ci_selective_layer_wiring.py b/tests/test_ci_selective_layer_wiring.py
index 9d320ddda4fc..e04c7216a02a 100644
--- a/tests/test_ci_selective_layer_wiring.py
+++ b/tests/test_ci_selective_layer_wiring.py
@@ -20,11 +20,11 @@ def step_by_name(job, name):
     return next(step for step in job["steps"] if step.get("name") == name)
 
 
-def test_layered_products_are_default_for_full_suite_transport():
+def test_aggregate_products_are_default_and_layers_opt_in():
     workflow = load()
     event = workflow.get("on", workflow.get(True))
     product = event["workflow_call"]["inputs"]["product_artifacts"]
-    assert product["default"] == "layered"
+    assert product["default"] == "aggregate"
     assert product["type"] == "string"
 
 
@@ -71,6 +71,6 @@ def test_consumers_prefer_warm_aggregate_then_selective_layers_before_remote_agg
 
 
 if __name__ == "__main__":
-    test_layered_products_are_default_for_full_suite_transport()
+    test_aggregate_products_are_default_and_layers_opt_in()
     test_compile_admission_publishes_exact_layer_index_outputs()
     test_consumers_prefer_warm_aggregate_then_selective_layers_before_remote_aggregate()