diff --git a/pkg/reconciler/revision/resources/deploy.go b/pkg/reconciler/revision/resources/deploy.go
index 117c5bd21ef0..13880c270033 100644
--- a/pkg/reconciler/revision/resources/deploy.go
+++ b/pkg/reconciler/revision/resources/deploy.go
@@ -138,15 +138,19 @@ func certVolume(secret string) corev1.Volume {
 	}
 }
 
-func rewriteUserLivenessProbe(p *corev1.Probe, userPort int) {
+func rewriteUserLivenessProbe(p *corev1.Probe, userPort int, allowCustomPort bool) {
 	if p == nil {
 		return
 	}
 	switch {
 	case p.HTTPGet != nil:
-		p.HTTPGet.Port = intstr.FromInt(userPort)
+		if !allowCustomPort || p.HTTPGet.Port.IntValue() == 0 {
+			p.HTTPGet.Port = intstr.FromInt(userPort)
+		}
 	case p.TCPSocket != nil:
-		p.TCPSocket.Port = intstr.FromInt(userPort)
+		if !allowCustomPort || p.TCPSocket.Port.IntValue() == 0 {
+			p.TCPSocket.Port = intstr.FromInt(userPort)
+		}
 	}
 }
 
@@ -206,7 +210,7 @@ func makePodSpec(rev *v1.Revision, cfg *config.Config) (*corev1.PodSpec, error)
 		extraVolumes = append(extraVolumes, certVolume(networking.ServingCertName))
 	}
 
-	podSpec := BuildPodSpec(rev, append(BuildUserContainers(rev), *queueContainer), cfg)
+	podSpec := BuildPodSpec(rev, append(BuildUserContainers(rev, cfg.Features), *queueContainer), cfg)
 	podSpec.Volumes = append(podSpec.Volumes, extraVolumes...)
 
 	if val := cfg.Deployment.PodRuntimeClassName(rev.ObjectMeta.Labels); podSpec.RuntimeClassName == nil {
@@ -237,12 +241,14 @@ func makePodSpec(rev *v1.Revision, cfg *config.Config) (*corev1.PodSpec, error)
 }
 
 // BuildUserContainers makes an array of containers from the Revision template.
-func BuildUserContainers(rev *v1.Revision) []corev1.Container {
+// features may be nil, in which case default behavior (strict port rewriting) is used.
+func BuildUserContainers(rev *v1.Revision, features *apiconfig.Features) []corev1.Container {
+	allowCustomPort := features != nil && features.MultiContainerProbing == apiconfig.Enabled
 	containers := make([]corev1.Container, 0, len(rev.Spec.PodSpec.Containers))
 	for i := range rev.Spec.PodSpec.Containers {
 		var container corev1.Container
 		if len(rev.Spec.PodSpec.Containers[i].Ports) != 0 || len(rev.Spec.PodSpec.Containers) == 1 {
-			container = makeServingContainer(*rev.Spec.PodSpec.Containers[i].DeepCopy(), rev)
+			container = makeServingContainer(*rev.Spec.PodSpec.Containers[i].DeepCopy(), rev, allowCustomPort)
 		} else {
 			container = makeContainer(*rev.Spec.PodSpec.Containers[i].DeepCopy(), rev)
 		}
@@ -283,7 +289,7 @@ func makeContainer(container corev1.Container, rev *v1.Revision) corev1.Containe
 	return container
 }
 
-func makeServingContainer(servingContainer corev1.Container, rev *v1.Revision) corev1.Container {
+func makeServingContainer(servingContainer corev1.Container, rev *v1.Revision, allowCustomPort bool) corev1.Container {
 	userPort := getUserPort(rev)
 	userPortStr := strconv.Itoa(int(userPort))
 	// Replacement is safe as only up to a single port is allowed on the Revision
@@ -291,7 +297,7 @@ func makeServingContainer(servingContainer corev1.Container, rev *v1.Revision) c
 	servingContainer.Env = append(servingContainer.Env, buildUserPortEnv(userPortStr))
 	container := makeContainer(servingContainer, rev)
 	// If the user provides a liveness probe, we should rewrite in the port on the user-container for them.
-	rewriteUserLivenessProbe(container.LivenessProbe, int(userPort))
+	rewriteUserLivenessProbe(container.LivenessProbe, int(userPort), allowCustomPort)
 	return container
 }
 
diff --git a/pkg/reconciler/revision/resources/deploy_test.go b/pkg/reconciler/revision/resources/deploy_test.go
index 73c16c0181a5..55a61165efcc 100644
--- a/pkg/reconciler/revision/resources/deploy_test.go
+++ b/pkg/reconciler/revision/resources/deploy_test.go
@@ -1077,6 +1077,161 @@ func TestMakePodSpec(t *testing.T) {
 				),
 				queueContainer(),
 			}),
+	}, {
+		name: "with HTTP liveness probe on custom port and multi-container-probing enabled",
+		fc: apicfg.Features{
+			MultiContainerProbing: apicfg.Enabled,
+		},
+		rev: revision("bar", "foo",
+			withContainers([]corev1.Container{{
+				Name:           servingContainerName,
+				Image:          "busybox",
+				ReadinessProbe: withTCPReadinessProbe(v1.DefaultUserPort),
+				LivenessProbe: &corev1.Probe{
+					ProbeHandler: corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/health",
+							Port: intstr.FromInt32(8081),
+						},
+					},
+				},
+			}}),
+			WithContainerStatuses([]v1.ContainerStatus{{
+				ImageDigest: "busybox@sha256:deadbeef",
+			}}),
+		),
+		want: podSpec(
+			[]corev1.Container{
+				servingContainer(
+					func(container *corev1.Container) {
+						container.Image = "busybox@sha256:deadbeef"
+					},
+					withLivenessProbe(corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/health",
+							Port: intstr.FromInt32(8081),
+						},
+					}),
+				),
+				queueContainer(
+					withEnvVar("ENABLE_MULTI_CONTAINER_PROBES", "true"),
+					withEnvVar("SERVING_READINESS_PROBE", `[{"tcpSocket":{"port":8080,"host":"127.0.0.1"}}]`),
+				),
+			}),
+	}, {
+		name: "with TCP liveness probe on custom port and multi-container-probing enabled",
+		fc: apicfg.Features{
+			MultiContainerProbing: apicfg.Enabled,
+		},
+		rev: revision("bar", "foo",
+			withContainers([]corev1.Container{{
+				Name:           servingContainerName,
+				Image:          "busybox",
+				ReadinessProbe: withTCPReadinessProbe(v1.DefaultUserPort),
+				LivenessProbe: &corev1.Probe{
+					ProbeHandler: corev1.ProbeHandler{
+						TCPSocket: &corev1.TCPSocketAction{
+							Port: intstr.FromInt32(8081),
+						},
+					},
+				},
+			}}),
+			WithContainerStatuses([]v1.ContainerStatus{{
+				ImageDigest: "busybox@sha256:deadbeef",
+			}}),
+		),
+		want: podSpec(
+			[]corev1.Container{
+				servingContainer(
+					func(container *corev1.Container) {
+						container.Image = "busybox@sha256:deadbeef"
+					},
+					withLivenessProbe(corev1.ProbeHandler{
+						TCPSocket: &corev1.TCPSocketAction{
+							Port: intstr.FromInt32(8081),
+						},
+					}),
+				),
+				queueContainer(
+					withEnvVar("ENABLE_MULTI_CONTAINER_PROBES", "true"),
+					withEnvVar("SERVING_READINESS_PROBE", `[{"tcpSocket":{"port":8080,"host":"127.0.0.1"}}]`),
+				),
+			}),
+	}, {
+		name: "with HTTP liveness probe without port and multi-container-probing enabled",
+		fc: apicfg.Features{
+			MultiContainerProbing: apicfg.Enabled,
+		},
+		rev: revision("bar", "foo",
+			withContainers([]corev1.Container{{
+				Name:           servingContainerName,
+				Image:          "busybox",
+				ReadinessProbe: withTCPReadinessProbe(v1.DefaultUserPort),
+				LivenessProbe: &corev1.Probe{
+					ProbeHandler: corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/",
+						},
+					},
+				},
+			}}),
+			WithContainerStatuses([]v1.ContainerStatus{{
+				ImageDigest: "busybox@sha256:deadbeef",
+			}}),
+		),
+		want: podSpec(
+			[]corev1.Container{
+				servingContainer(
+					func(container *corev1.Container) {
+						container.Image = "busybox@sha256:deadbeef"
+					},
+					withLivenessProbe(corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/",
+							Port: intstr.FromInt32(v1.DefaultUserPort),
+						},
+					}),
+				),
+				queueContainer(
+					withEnvVar("ENABLE_MULTI_CONTAINER_PROBES", "true"),
+					withEnvVar("SERVING_READINESS_PROBE", `[{"tcpSocket":{"port":8080,"host":"127.0.0.1"}}]`),
+				),
+			}),
+	}, {
+		name: "with HTTP liveness probe on custom port and multi-container-probing disabled",
+		rev: revision("bar", "foo",
+			withContainers([]corev1.Container{{
+				Name:           servingContainerName,
+				Image:          "busybox",
+				ReadinessProbe: withTCPReadinessProbe(v1.DefaultUserPort),
+				LivenessProbe: &corev1.Probe{
+					ProbeHandler: corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/health",
+							Port: intstr.FromInt32(8081),
+						},
+					},
+				},
+			}}),
+			WithContainerStatuses([]v1.ContainerStatus{{
+				ImageDigest: "busybox@sha256:deadbeef",
+			}}),
+		),
+		want: podSpec(
+			[]corev1.Container{
+				servingContainer(
+					func(container *corev1.Container) {
+						container.Image = "busybox@sha256:deadbeef"
+					},
+					withLivenessProbe(corev1.ProbeHandler{
+						HTTPGet: &corev1.HTTPGetAction{
+							Path: "/health",
+							Port: intstr.FromInt32(v1.DefaultUserPort),
+						},
+					}),
+				),
+				queueContainer(),
+			}),
 	}, {
 		name: "with HTTP startup probe",
 		rev: revision("bar", "foo",
diff --git a/pkg/webhook/podspec_dryrun.go b/pkg/webhook/podspec_dryrun.go
index 852efc101b61..07081fc1455d 100644
--- a/pkg/webhook/podspec_dryrun.go
+++ b/pkg/webhook/podspec_dryrun.go
@@ -59,7 +59,7 @@ func validatePodSpec(ctx context.Context, ps v1.RevisionSpec, namespace string)
 		Spec:       ps,
 	}
 	rev.SetDefaults(ctx)
-	podSpec := resources.BuildPodSpec(rev, resources.BuildUserContainers(rev), nil /*configs*/)
+	podSpec := resources.BuildPodSpec(rev, resources.BuildUserContainers(rev, nil /*features*/), nil /*configs*/)
 
 	// Make a sample pod with the template Revisions & PodSpec and dryrun call to API-server
 	pod := &corev1.Pod{