diff --git a/pkg/controlplane/apiserver/aggregator.go b/pkg/controlplane/apiserver/aggregator.go
index 690bcae56cf75..6aec4fab7db41 100644
--- a/pkg/controlplane/apiserver/aggregator.go
+++ b/pkg/controlplane/apiserver/aggregator.go
@@ -21,6 +21,7 @@ import (
 	"net/http"
 	"strings"
 	"sync"
+	"time"
 
 	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	apiextensionsinformers "k8s.io/apiextensions-apiserver/pkg/client/informers/externalversions/apiextensions/v1"
@@ -196,6 +197,22 @@ func CreateAggregatorServer(aggregatorConfig aggregatorapiserver.CompletedConfig
 		return nil, err
 	}
 
+	// temporary hook to prove the pre-ready request window exists on 1.35.
+	// This hook is registered on the aggregator's GenericAPIServer so its readyz check
+	// blocks the aggregator's /readyz endpoint.
+	//
+	// This simulates the readiness delay that storage-readiness causes on 1.36, which
+	// propagates through apiservice-wait-for-first-sync to block the aggregator's HasBeenReady.
+	// A hook on the kube-apiserver level does NOT work because its readyz check is on
+	// the kube-apiserver's mux, which is shadowed by the aggregator's /readyz handler.
+	aggregatorServer.GenericAPIServer.AddPostStartHookOrDie("prove-pre-ready-window", func(hookContext genericapiserver.PostStartHookContext) error {
+		select {
+		case <-time.After(5 * time.Second):
+		case <-hookContext.Done():
+		}
+		return nil
+	})
+
 	err = aggregatorServer.GenericAPIServer.AddBootSequenceHealthChecks(
 		makeAPIServiceAvailableHealthCheck(
 			"autoregister-completion",
diff --git a/staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go b/staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go
index 0cb1007495741..03bca2ab2e13d 100644
--- a/staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go
+++ b/staging/src/k8s.io/apiserver/pkg/server/genericapiserver.go
@@ -593,7 +593,7 @@ func (s preparedGenericAPIServer) RunWithContext(ctx context.Context) error {
 		Listener:   s.SecureServingInfo.Listener,
 		lateStopCh: lateStopCh,
 	}
-	unexpectedRequestsEventf.Store(s.Eventf)
+	unexpectedRequestsEventf.Store(eventfFunc(s.Eventf))
 
 	// close socket after delayed stopCh
 	shutdownTimeout := s.ShutdownTimeout