diff --git a/cmd/jobsink/main.go b/cmd/jobsink/main.go
index 4e796c4dea5..162324df25f 100644
--- a/cmd/jobsink/main.go
+++ b/cmd/jobsink/main.go
@@ -257,6 +257,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	js = js.DeepCopy() // Do not modify informer copy.
+	js.SetDefaults(ctx)
+
 	job := js.Spec.Job.DeepCopy()
 	job.Name = jobName
 	if job.Labels == nil {
diff --git a/pkg/apis/sinks/v1alpha1/job_sink_defaults.go b/pkg/apis/sinks/v1alpha1/job_sink_defaults.go
index 13f62e868b9..3bd18fbf3f0 100644
--- a/pkg/apis/sinks/v1alpha1/job_sink_defaults.go
+++ b/pkg/apis/sinks/v1alpha1/job_sink_defaults.go
@@ -18,7 +18,48 @@ package v1alpha1
 
 import (
 	"context"
+
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
 )
 
 func (sink *JobSink) SetDefaults(ctx context.Context) {
+	if sink.Spec.Job != nil {
+		setBatchJobDefaults(sink.Spec.Job)
+	}
+}
+
+func setBatchJobDefaults(job *batchv1.Job) {
+	for i := range job.Spec.Template.Spec.Containers {
+		executionModeFound := false
+		for j := range job.Spec.Template.Spec.Containers[i].Env {
+			if job.Spec.Template.Spec.Containers[i].Env[j].Name == ExecutionModeEnvVar {
+				executionModeFound = true
+				break
+			}
+		}
+		if executionModeFound {
+			continue
+		}
+		job.Spec.Template.Spec.Containers[i].Env = append(job.Spec.Template.Spec.Containers[i].Env, corev1.EnvVar{
+			Name:  ExecutionModeEnvVar,
+			Value: string(ExecutionModeBatch),
+		})
+	}
+	for i := range job.Spec.Template.Spec.InitContainers {
+		executionModeFound := false
+		for j := range job.Spec.Template.Spec.InitContainers[i].Env {
+			if job.Spec.Template.Spec.InitContainers[i].Env[j].Name == ExecutionModeEnvVar {
+				executionModeFound = true
+				break
+			}
+		}
+		if executionModeFound {
+			continue
+		}
+		job.Spec.Template.Spec.InitContainers[i].Env = append(job.Spec.Template.Spec.InitContainers[i].Env, corev1.EnvVar{
+			Name:  ExecutionModeEnvVar,
+			Value: string(ExecutionModeBatch),
+		})
+	}
 }
diff --git a/pkg/apis/sinks/v1alpha1/job_sink_defaults_test.go b/pkg/apis/sinks/v1alpha1/job_sink_defaults_test.go
index 9df0edde347..766ab45b0d6 100644
--- a/pkg/apis/sinks/v1alpha1/job_sink_defaults_test.go
+++ b/pkg/apis/sinks/v1alpha1/job_sink_defaults_test.go
@@ -21,13 +21,111 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
 )
 
 func TestSetDefaults(t *testing.T) {
 	testCases := map[string]struct {
 		initial  JobSink
 		expected JobSink
-	}{}
+	}{
+		"execution mode": {
+			initial: JobSink{
+				Spec: JobSinkSpec{
+					Job: &batchv1.Job{
+						Spec:       batchv1.JobSpec{
+							Template: corev1.PodTemplateSpec{
+								Spec:       corev1.PodSpec{
+									Containers: []corev1.Container{
+										{
+											Name:                     "cnt",
+											Image:                    "img",
+										},
+										{
+											Name:                     "cnt2",
+											Image:                    "img2",
+										},
+										{
+											Name:                     "cnt3",
+											Image:                    "img3",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "something"},
+											},
+										},
+									},
+									InitContainers: []corev1.Container{
+										{
+											Name:                     "cnt",
+											Image:                    "img",
+										},
+										{
+											Name:                     "cnt-ini2",
+											Image:                    "img-ini2",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "something"},
+											},
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			expected: JobSink{
+				Spec: JobSinkSpec{
+					Job: &batchv1.Job{
+						Spec:       batchv1.JobSpec{
+							Template: corev1.PodTemplateSpec{
+								Spec:       corev1.PodSpec{
+									InitContainers: []corev1.Container{
+										{
+											Name:                     "cnt",
+											Image:                    "img",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "batch"},
+											},
+										},
+										{
+											Name:                     "cnt-ini2",
+											Image:                    "img-ini2",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "something"},
+											},
+										},
+									},
+									Containers: []corev1.Container{
+										{
+											Name:                     "cnt",
+											Image:                    "img",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "batch"},
+											},
+										},
+										{
+											Name:                     "cnt2",
+											Image:                    "img2",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "batch"},
+											},
+										},
+										{
+											Name:                     "cnt3",
+											Image:                    "img3",
+											Env: []corev1.EnvVar{
+												{Name: "KNATIVE_EXECUTION_MODE", Value: "something"},
+											},
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
 	for n, tc := range testCases {
 		t.Run(n, func(t *testing.T) {
 			tc.initial.SetDefaults(context.TODO())
diff --git a/pkg/apis/sinks/v1alpha1/job_sink_types.go b/pkg/apis/sinks/v1alpha1/job_sink_types.go
index 857e9f79a17..da69766bdd0 100644
--- a/pkg/apis/sinks/v1alpha1/job_sink_types.go
+++ b/pkg/apis/sinks/v1alpha1/job_sink_types.go
@@ -22,9 +22,20 @@ import (
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
-	eventingduckv1 "knative.dev/eventing/pkg/apis/duck/v1"
 	duckv1 "knative.dev/pkg/apis/duck/v1"
 	"knative.dev/pkg/kmeta"
+
+	eventingduckv1 "knative.dev/eventing/pkg/apis/duck/v1"
+)
+
+const (
+	ExecutionModeEnvVar = "KNATIVE_EXECUTION_MODE"
+)
+
+type ExecutionMode string
+
+const (
+	ExecutionModeBatch ExecutionMode = "batch"
 )
 
 // +genclient
diff --git a/pkg/reconciler/jobsink/jobsink_test.go b/pkg/reconciler/jobsink/jobsink_test.go
index fba76c2ef10..5ee0d119f65 100644
--- a/pkg/reconciler/jobsink/jobsink_test.go
+++ b/pkg/reconciler/jobsink/jobsink_test.go
@@ -263,6 +263,9 @@ func testJob(name string) *batchv1.Job {
 					Containers: []corev1.Container{
 						{
 							Name: "test-container",
+							Env: []corev1.EnvVar{
+								{Name: "KNATIVE_EXECUTION_MODE", Value: "batch"},
+							},
 						},
 					},
 				},