diff --git a/config/core/configmaps/features.yaml b/config/core/configmaps/features.yaml
index c01121a1e4eb..287a4be8c3e5 100644
--- a/config/core/configmaps/features.yaml
+++ b/config/core/configmaps/features.yaml
@@ -20,7 +20,7 @@ metadata:
   labels:
     serving.knative.dev/release: devel
   annotations:
-    knative.dev/example-checksum: "983ddf13"
+    knative.dev/example-checksum: "c0b41539"
 data:
   _example: |
     ################################
@@ -62,6 +62,10 @@ data:
     #   attaching the following metadata annotation: "features.knative.dev/podspec-dryrun":"enabled".
     kubernetes.podspec-dryrun: "allowed"
 
+    # When set to "enabled" or "allowed" this feature allows end-users to set
+    # the Pod's RuntimeClassName.
+    kubernetes.podspec-runtimeclassname: "disabled"
+
     # This feature allows end-users to set a subset of fields on the Pod's SecurityContext
     # in addition to expanding the allowable fields within a Container's SecurityContext.
     #
diff --git a/pkg/apis/config/features.go b/pkg/apis/config/features.go
index 10bde135f6d2..4174ff112790 100644
--- a/pkg/apis/config/features.go
+++ b/pkg/apis/config/features.go
@@ -40,15 +40,16 @@ const (
 
 func defaultFeaturesConfig() *Features {
 	return &Features{
-		MultiContainer:         Enabled,
-		PodSpecAffinity:        Disabled,
-		PodSpecFieldRef:        Disabled,
-		PodSpecDryRun:          Allowed,
-		PodSpecNodeSelector:    Disabled,
-		PodSpecSecurityContext: Disabled,
-		PodSpecTolerations:     Disabled,
-		ResponsiveRevisionGC:   Disabled,
-		TagHeaderBasedRouting:  Disabled,
+		MultiContainer:          Enabled,
+		PodSpecAffinity:         Disabled,
+		PodSpecDryRun:           Allowed,
+		PodSpecFieldRef:         Disabled,
+		PodSpecNodeSelector:     Disabled,
+		PodSpecRuntimeClassName: Disabled,
+		PodSpecSecurityContext:  Disabled,
+		PodSpecTolerations:      Disabled,
+		ResponsiveRevisionGC:    Disabled,
+		TagHeaderBasedRouting:   Disabled,
 	}
 }
 
@@ -59,9 +60,10 @@ func NewFeaturesConfigFromMap(data map[string]string) (*Features, error) {
 	if err := cm.Parse(data,
 		asFlag("multi-container", &nc.MultiContainer),
 		asFlag("kubernetes.podspec-affinity", &nc.PodSpecAffinity),
-		asFlag("kubernetes.podspec-fieldref", &nc.PodSpecFieldRef),
 		asFlag("kubernetes.podspec-dryrun", &nc.PodSpecDryRun),
+		asFlag("kubernetes.podspec-fieldref", &nc.PodSpecFieldRef),
 		asFlag("kubernetes.podspec-nodeselector", &nc.PodSpecNodeSelector),
+		asFlag("kubernetes.podspec-runtimeclassname", &nc.PodSpecRuntimeClassName),
 		asFlag("kubernetes.podspec-securitycontext", &nc.PodSpecSecurityContext),
 		asFlag("kubernetes.podspec-tolerations", &nc.PodSpecTolerations),
 		asFlag("responsive-revision-gc", &nc.ResponsiveRevisionGC),
@@ -78,15 +80,16 @@ func NewFeaturesConfigFromConfigMap(config *corev1.ConfigMap) (*Features, error)
 
 // Features specifies which features are allowed by the webhook.
 type Features struct {
-	MultiContainer         Flag
-	PodSpecAffinity        Flag
-	PodSpecFieldRef        Flag
-	PodSpecDryRun          Flag
-	PodSpecNodeSelector    Flag
-	PodSpecTolerations     Flag
-	PodSpecSecurityContext Flag
-	ResponsiveRevisionGC   Flag
-	TagHeaderBasedRouting  Flag
+	MultiContainer          Flag
+	PodSpecAffinity         Flag
+	PodSpecDryRun           Flag
+	PodSpecFieldRef         Flag
+	PodSpecNodeSelector     Flag
+	PodSpecRuntimeClassName Flag
+	PodSpecSecurityContext  Flag
+	PodSpecTolerations      Flag
+	ResponsiveRevisionGC    Flag
+	TagHeaderBasedRouting   Flag
 }
 
 // asFlag parses the value at key as a Flag into the target, if it exists.
diff --git a/pkg/apis/config/features_test.go b/pkg/apis/config/features_test.go
index f43e059d58f6..587040546262 100644
--- a/pkg/apis/config/features_test.go
+++ b/pkg/apis/config/features_test.go
@@ -59,24 +59,26 @@ func TestFeaturesConfiguration(t *testing.T) {
 		name:    "features Enabled",
 		wantErr: false,
 		wantFeatures: defaultWith(&Features{
-			MultiContainer:         Enabled,
-			PodSpecAffinity:        Enabled,
-			PodSpecDryRun:          Enabled,
-			PodSpecNodeSelector:    Enabled,
-			PodSpecSecurityContext: Enabled,
-			PodSpecTolerations:     Enabled,
-			ResponsiveRevisionGC:   Enabled,
-			TagHeaderBasedRouting:  Enabled,
+			MultiContainer:          Enabled,
+			PodSpecAffinity:         Enabled,
+			PodSpecDryRun:           Enabled,
+			PodSpecNodeSelector:     Enabled,
+			PodSpecRuntimeClassName: Enabled,
+			PodSpecSecurityContext:  Enabled,
+			PodSpecTolerations:      Enabled,
+			ResponsiveRevisionGC:    Enabled,
+			TagHeaderBasedRouting:   Enabled,
 		}),
 		data: map[string]string{
-			"multi-container":                    "Enabled",
-			"kubernetes.podspec-affinity":        "Enabled",
-			"kubernetes.podspec-dryrun":          "Enabled",
-			"kubernetes.podspec-nodeselector":    "Enabled",
-			"kubernetes.podspec-securitycontext": "Enabled",
-			"kubernetes.podspec-tolerations":     "Enabled",
-			"responsive-revision-gc":             "Enabled",
-			"tag-header-based-routing":           "Enabled",
+			"multi-container":                     "Enabled",
+			"kubernetes.podspec-affinity":         "Enabled",
+			"kubernetes.podspec-dryrun":           "Enabled",
+			"kubernetes.podspec-nodeselector":     "Enabled",
+			"kubernetes.podspec-runtimeclassname": "Enabled",
+			"kubernetes.podspec-securitycontext":  "Enabled",
+			"kubernetes.podspec-tolerations":      "Enabled",
+			"responsive-revision-gc":              "Enabled",
+			"tag-header-based-routing":            "Enabled",
 		},
 	}, {
 		name:    "multi-container Allowed",
@@ -186,6 +188,33 @@ func TestFeaturesConfiguration(t *testing.T) {
 		data: map[string]string{
 			"kubernetes.podspec-nodeselector": "Disabled",
 		},
+	}, {
+		name:    "kubernetes.podspec-runtimeclassname Allowed",
+		wantErr: false,
+		wantFeatures: defaultWith(&Features{
+			PodSpecRuntimeClassName: Allowed,
+		}),
+		data: map[string]string{
+			"kubernetes.podspec-runtimeclassname": "Allowed",
+		},
+	}, {
+		name:    "kubernetes.podspec-runtimeclassname Enabled",
+		wantErr: false,
+		wantFeatures: defaultWith(&Features{
+			PodSpecRuntimeClassName: Enabled,
+		}),
+		data: map[string]string{
+			"kubernetes.podspec-runtimeclassname": "Enabled",
+		},
+	}, {
+		name:    "kubernetes.podspec-runtimeclassname Disabled",
+		wantErr: false,
+		wantFeatures: defaultWith(&Features{
+			PodSpecRuntimeClassName: Disabled,
+		}),
+		data: map[string]string{
+			"kubernetes.podspec-runtimeclassname": "Disabled",
+		},
 	}, {
 		name:    "kubernetes.podspec-tolerations Allowed",
 		wantErr: false,
diff --git a/pkg/apis/serving/fieldmask.go b/pkg/apis/serving/fieldmask.go
index aa3ee98b1abe..f345031f55f6 100644
--- a/pkg/apis/serving/fieldmask.go
+++ b/pkg/apis/serving/fieldmask.go
@@ -161,6 +161,9 @@ func PodSpecMask(ctx context.Context, in *corev1.PodSpec) *corev1.PodSpec {
 	if cfg.Features.PodSpecNodeSelector != config.Disabled {
 		out.NodeSelector = in.NodeSelector
 	}
+	if cfg.Features.PodSpecRuntimeClassName != config.Disabled {
+		out.RuntimeClassName = in.RuntimeClassName
+	}
 	if cfg.Features.PodSpecTolerations != config.Disabled {
 		out.Tolerations = in.Tolerations
 	}
@@ -189,7 +192,6 @@ func PodSpecMask(ctx context.Context, in *corev1.PodSpec) *corev1.PodSpec {
 	out.Priority = nil
 	out.DNSConfig = nil
 	out.ReadinessGates = nil
-	out.RuntimeClassName = nil
 
 	return out
 }
diff --git a/pkg/apis/serving/k8s_validation_test.go b/pkg/apis/serving/k8s_validation_test.go
index dfd0643c460b..b51e507865e7 100644
--- a/pkg/apis/serving/k8s_validation_test.go
+++ b/pkg/apis/serving/k8s_validation_test.go
@@ -69,6 +69,13 @@ func withPodSpecTolerationsEnabled() configOption {
 	}
 }
 
+func withPodSpecRuntimeClassNameEnabled() configOption {
+	return func(cfg *config.Config) *config.Config {
+		cfg.Features.PodSpecRuntimeClassName = config.Enabled
+		return cfg
+	}
+}
+
 func withPodSpecSecurityContextEnabled() configOption {
 	return func(cfg *config.Config) *config.Config {
 		cfg.Features.PodSpecSecurityContext = config.Enabled
@@ -543,6 +550,8 @@ func TestPodSpecMultiContainerValidation(t *testing.T) {
 }
 
 func TestPodSpecFeatureValidation(t *testing.T) {
+	runtimeClassName := "test"
+
 	featureData := []struct {
 		name        string
 		featureSpec corev1.PodSpec
@@ -597,6 +606,16 @@ func TestPodSpecFeatureValidation(t *testing.T) {
 			Paths:   []string{"tolerations"},
 		},
 		cfgOpts: []configOption{withPodSpecTolerationsEnabled()},
+	}, {
+		name: "RuntimeClassName",
+		featureSpec: corev1.PodSpec{
+			RuntimeClassName: &runtimeClassName,
+		},
+		err: &apis.FieldError{
+			Message: "must not set the field(s)",
+			Paths:   []string{"runtimeClassName"},
+		},
+		cfgOpts: []configOption{withPodSpecRuntimeClassNameEnabled()},
 	}, {
 		name: "PodSpecSecurityContext",
 		featureSpec: corev1.PodSpec{