diff --git a/generic-argo-apps-chart/templates/genericTemplate.yaml b/generic-argo-apps-chart/templates/genericTemplate.yaml
index 95ac7c0..1f2ecea 100644
--- a/generic-argo-apps-chart/templates/genericTemplate.yaml
+++ b/generic-argo-apps-chart/templates/genericTemplate.yaml
@@ -24,11 +24,26 @@
 
 {{ $argoAppNamespace := $top.Values.argocdSpec.namespace }}
 
+{{- $compareOptions := $config.compareOptions | default list -}}
+
 apiVersion: argoproj.io/v1alpha1
 kind: Application
 metadata:
   name: '{{- if $appNameOverride }}{{ $appNameOverride }}{{- else }}{{ printf "%s-%s-%s" $appName $cluster $env }}{{- end }}'
   namespace: {{ $argoAppNamespace }}
+{{- if $compareOptions }}
+  annotations:
+    # Opt-in per appSpec entry, as a list of Argo CD compare options.
+    #
+    # The one that matters here is ServerSideDiff=true, which is the escape
+    # hatch for "field not declared in schema" diff failures. Argo CD
+    # normally computes the diff locally against a Kubernetes schema baked
+    # into its own binary, so a cluster newer than Argo CD has fields Argo
+    # CD has never heard of and the diff aborts. This option asks the API
+    # server to compute the diff instead (a dry-run apply), and the API
+    # server necessarily knows its own fields.
+    argocd.argoproj.io/compare-options: {{ join "," $compareOptions | quote }}
+{{- end }}
   labels:
 {{ toYaml $labels | indent 4 }}
   finalizers:
diff --git a/values/incubator-infra-gke-toolshed-prd-usc1-values.yaml b/values/incubator-infra-gke-toolshed-prd-usc1-values.yaml
index 8122840..9eb8c10 100644
--- a/values/incubator-infra-gke-toolshed-prd-usc1-values.yaml
+++ b/values/incubator-infra-gke-toolshed-prd-usc1-values.yaml
@@ -51,6 +51,19 @@ appSpec:
     # Contour's HTTPProxy CRD embeds a large schema, same 256KiB
     # last-applied-configuration problem as cert-manager's.
     serverSideApply: true
+    # Required alongside serverSideApply on this cluster. That sync option
+    # makes Argo CD compute the diff with the Kubernetes schema compiled
+    # into its own binary, and Argo CD v2.13 predates this cluster: live
+    # Deployments here carry status.terminatingReplicas, beta and enabled by
+    # default since Kubernetes 1.33, which that schema has never heard of.
+    # The diff then aborts with "field not declared in schema" and the app
+    # can neither be compared nor synced. ServerSideDiff hands the diff to
+    # the API server, which necessarily knows its own fields.
+    #
+    # This is a workaround for an out-of-date Argo CD, not a fix. The fix is
+    # upgrading Argo CD to a build whose schema matches the cluster.
+    compareOptions:
+      - ServerSideDiff=true
   - name: vault
     # Fresh install here, unlike the homelab's adoption of a running Vault.
     # nameOverride pinned so the release is "vault" in namespace "vault":
@@ -70,6 +83,10 @@ appSpec:
     # cert-manager's CRDs embed large OpenAPI schemas; SSA avoids the
     # 256KiB last-applied-configuration limit, same as external-secrets.
     serverSideApply: true
+    # See the contour entry above: server-side apply diffs against Argo CD's
+    # own bundled schema, which is older than this cluster.
+    compareOptions:
+      - ServerSideDiff=true
   - name: external-secrets
     # Every credential in the cluster arrives through this. nameOverride is
     # not cosmetic here: without it the release becomes
@@ -84,6 +101,10 @@ appSpec:
     # ClusterSecretStore's CRD embeds a large provider schema and exceeds
     # the 256KiB annotation limit on a client-side apply.
     serverSideApply: true
+    # See the contour entry above: server-side apply diffs against Argo CD's
+    # own bundled schema, which is older than this cluster.
+    compareOptions:
+      - ServerSideDiff=true
   - name: harbor
     # Object names are all prefixed with the release name, and the pipeline
     # refers to them, so it is pinned.