diff --git a/platform/apps/kube-prometheus-stack/application.yaml b/platform/apps/kube-prometheus-stack/application.yaml
index 2bdb589..31fe23a 100644
--- a/platform/apps/kube-prometheus-stack/application.yaml
+++ b/platform/apps/kube-prometheus-stack/application.yaml
@@ -25,6 +25,17 @@ spec:
   destination:
     server: https://kubernetes.default.svc
     namespace: monitoring
+  # Gateway API's admission webhook server-side-defaults backendRefs[].group
+  # and .weight on the grafana HTTPRoute — fields our manifest omits — so
+  # ArgoCD sees permanent drift vs Git even though the object matches intent
+  # (route itself is Accepted/ResolvedRefs=True, Grafana reachable). Ignore
+  # the defaulted fields instead of chasing a diff that will never close.
+  ignoreDifferences:
+    - group: gateway.networking.k8s.io
+      kind: HTTPRoute
+      jsonPointers:
+        - /spec/rules/0/backendRefs/0/group
+        - /spec/rules/0/backendRefs/0/weight
   syncPolicy:
     automated:
       prune: true