diff --git a/pkg/apis/eventing/v1/broker_validation.go b/pkg/apis/eventing/v1/broker_validation.go
index e7e0e8a3c46..404545216ad 100644
--- a/pkg/apis/eventing/v1/broker_validation.go
+++ b/pkg/apis/eventing/v1/broker_validation.go
@@ -29,7 +29,14 @@ const (
 
 func (b *Broker) Validate(ctx context.Context) *apis.FieldError {
 	withNS := apis.AllowDifferentNamespace(apis.WithinParent(ctx, b.ObjectMeta))
-	return b.Spec.Validate(withNS).ViaField("spec")
+
+	// Make sure a BrokerClassAnnotation exists
+	var errs *apis.FieldError
+	if bc, ok := b.GetAnnotations()[BrokerClassAnnotationKey]; !ok || bc == "" {
+		errs = errs.Also(apis.ErrMissingField(BrokerClassAnnotationKey))
+	}
+
+	return errs.Also(b.Spec.Validate(withNS).ViaField("spec"))
 }
 
 func (bs *BrokerSpec) Validate(ctx context.Context) *apis.FieldError {
diff --git a/pkg/apis/eventing/v1/broker_validation_test.go b/pkg/apis/eventing/v1/broker_validation_test.go
index 774d55fd27a..3f26a469b4f 100644
--- a/pkg/apis/eventing/v1/broker_validation_test.go
+++ b/pkg/apis/eventing/v1/broker_validation_test.go
@@ -46,11 +46,11 @@ func TestBrokerImmutableFields(t *testing.T) {
 		"nil original": {
 			wantErr: nil,
 		},
-		"no ChannelTemplateSpec mutation": {
+		"no BrokerClassAnnotation mutation": {
 			og:      current,
 			wantErr: nil,
 		},
-		"ChannelTemplateSpec mutated": {
+		"BrokerClassAnnotation mutated": {
 			og: original,
 			wantErr: &apis.FieldError{
 				Message: "Immutable fields changed (-old +new)",
@@ -80,11 +80,30 @@ func TestValidate(t *testing.T) {
 		b    Broker
 		want *apis.FieldError
 	}{{
-		name: "valid empty",
+		name: "missing annotation",
 		b:    Broker{},
+		want: apis.ErrMissingField("eventing.knative.dev/broker.class"),
+	}, {
+		name: "empty annotation",
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": ""},
+			},
+		},
+		want: apis.ErrMissingField("eventing.knative.dev/broker.class"),
+	}, {
+		name: "valid empty",
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
+		},
 	}, {
 		name: "valid config",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -97,6 +116,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "valid config, no namespace",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Name:       "name",
@@ -108,6 +130,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing name",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -120,6 +145,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing apiVersion",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace: "namespace",
@@ -132,6 +160,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing kind",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -144,6 +175,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid delivery, invalid delay string",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Delivery: &eventingduckv1.DeliverySpec{
 					BackoffDelay: &invalidString,
@@ -151,12 +185,12 @@ func TestValidate(t *testing.T) {
 			},
 		},
 		want: apis.ErrInvalidValue(invalidString, "spec.delivery.backoffDelay"),
-	}, {}}
+	}}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			got := test.b.Validate(context.Background())
 			if diff := cmp.Diff(test.want.Error(), got.Error()); diff != "" {
-				t.Errorf("BrokerSpec.Validate (-want, +got) = %v", diff)
+				t.Errorf("Broker.Validate (-want, +got) = %v", diff)
 			}
 		})
 	}
diff --git a/pkg/apis/eventing/v1beta1/broker_validation.go b/pkg/apis/eventing/v1beta1/broker_validation.go
index a3cac84d95f..7f408c48829 100644
--- a/pkg/apis/eventing/v1beta1/broker_validation.go
+++ b/pkg/apis/eventing/v1beta1/broker_validation.go
@@ -29,7 +29,14 @@ const (
 
 func (b *Broker) Validate(ctx context.Context) *apis.FieldError {
 	withNS := apis.AllowDifferentNamespace(apis.WithinParent(ctx, b.ObjectMeta))
-	return b.Spec.Validate(withNS).ViaField("spec")
+
+	// Make sure a BrokerClassAnnotation exists
+	var errs *apis.FieldError
+	if bc, ok := b.GetAnnotations()[BrokerClassAnnotationKey]; !ok || bc == "" {
+		errs = errs.Also(apis.ErrMissingField(BrokerClassAnnotationKey))
+	}
+
+	return errs.Also(b.Spec.Validate(withNS).ViaField("spec"))
 }
 
 func (bs *BrokerSpec) Validate(ctx context.Context) *apis.FieldError {
diff --git a/pkg/apis/eventing/v1beta1/broker_validation_test.go b/pkg/apis/eventing/v1beta1/broker_validation_test.go
index 4a73e3c89e9..4e0a473d578 100644
--- a/pkg/apis/eventing/v1beta1/broker_validation_test.go
+++ b/pkg/apis/eventing/v1beta1/broker_validation_test.go
@@ -46,11 +46,11 @@ func TestBrokerImmutableFields(t *testing.T) {
 		"nil original": {
 			wantErr: nil,
 		},
-		"no ChannelTemplateSpec mutation": {
+		"no BrokerClassAnnotation mutation": {
 			og:      current,
 			wantErr: nil,
 		},
-		"ChannelTemplateSpec mutated": {
+		"BrokerClassAnnotation mutated": {
 			og: original,
 			wantErr: &apis.FieldError{
 				Message: "Immutable fields changed (-old +new)",
@@ -80,11 +80,30 @@ func TestValidate(t *testing.T) {
 		b    Broker
 		want *apis.FieldError
 	}{{
-		name: "valid empty",
+		name: "missing annotation",
 		b:    Broker{},
+		want: apis.ErrMissingField("eventing.knative.dev/broker.class"),
+	}, {
+		name: "empty annotation",
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": ""},
+			},
+		},
+		want: apis.ErrMissingField("eventing.knative.dev/broker.class"),
+	}, {
+		name: "valid empty",
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
+		},
 	}, {
 		name: "valid config",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -97,6 +116,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "valid config, no namespace",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Name:       "name",
@@ -108,6 +130,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing name",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -120,6 +145,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing apiVersion",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace: "namespace",
@@ -132,6 +160,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid config, missing kind",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Config: &duckv1.KReference{
 					Namespace:  "namespace",
@@ -144,6 +175,9 @@ func TestValidate(t *testing.T) {
 	}, {
 		name: "invalid delivery, invalid delay string",
 		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+			},
 			Spec: BrokerSpec{
 				Delivery: &eventingduckv1beta1.DeliverySpec{
 					BackoffDelay: &invalidString,
@@ -151,12 +185,12 @@ func TestValidate(t *testing.T) {
 			},
 		},
 		want: apis.ErrInvalidValue(invalidString, "spec.delivery.backoffDelay"),
-	}, {}}
+	}}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			got := test.b.Validate(context.Background())
 			if diff := cmp.Diff(test.want.Error(), got.Error()); diff != "" {
-				t.Errorf("BrokerSpec.Validate (-want, +got) = %v", diff)
+				t.Errorf("Broker.Validate (-want, +got) = %v", diff)
 			}
 		})
 	}
diff --git a/pkg/reconciler/mtnamespace/resources/broker.go b/pkg/reconciler/mtnamespace/resources/broker.go
index 2c0c5fedd88..3b6273ac798 100644
--- a/pkg/reconciler/mtnamespace/resources/broker.go
+++ b/pkg/reconciler/mtnamespace/resources/broker.go
@@ -31,6 +31,7 @@ const (
 func MakeBroker(ns *corev1.Namespace) *v1beta1.Broker {
 	return &v1beta1.Broker{
 		ObjectMeta: metav1.ObjectMeta{
+			Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
 			OwnerReferences: []metav1.OwnerReference{
 				*metav1.NewControllerRef(ns.GetObjectMeta(), schema.GroupVersionKind{
 					Group:   corev1.SchemeGroupVersion.Group,