diff --git a/mmv1/products/compute/Subnetwork.yaml b/mmv1/products/compute/Subnetwork.yaml
index 036cc8cb3019..c15b6e3ca304 100644
--- a/mmv1/products/compute/Subnetwork.yaml
+++ b/mmv1/products/compute/Subnetwork.yaml
@@ -392,7 +392,7 @@ properties:
       The internal IPv6 address range that is assigned to this subnetwork.
   - !ruby/object:Api::Type::String
     name: 'externalIpv6Prefix'
-    output: true
+    default_from_api: true
     description: |
       The range of external IPv6 addresses that are owned by this subnetwork.
   - !ruby/object:Api::Type::Boolean