diff --git a/grpc/pb/phased_test.go b/grpc/pb/phased_test.go
new file mode 100644
index 0000000..c1924cc
--- /dev/null
+++ b/grpc/pb/phased_test.go
@@ -0,0 +1,23 @@
+package pb
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+// A phased update is flagged on the wire; an ordinary one carries no field at
+// all, so an old server or agent sees exactly the shape it always did.
+func TestPackageUpdatePhasedOnWire(t *testing.T) {
+	b, err := json.Marshal(PackageUpdate{Name: "libkrb5-3", NewVersion: "1.20", Phased: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(b), `"phased":true`) {
+		t.Fatalf("phased missing: %s", b)
+	}
+	b, _ = json.Marshal(PackageUpdate{Name: "curl", NewVersion: "8"})
+	if strings.Contains(string(b), "phased") {
+		t.Fatalf("an ordinary update must not carry phased: %s", b)
+	}
+}
diff --git a/grpc/pb/vantage.pb.go b/grpc/pb/vantage.pb.go
index 6d148c5..ee506d8 100644
--- a/grpc/pb/vantage.pb.go
+++ b/grpc/pb/vantage.pb.go
@@ -85,6 +85,10 @@ type PackageUpdate struct {
 	Name           string `json:"name"`
 	CurrentVersion string `json:"current_version,omitempty"`
 	NewVersion     string `json:"new_version"`
+	// Phased marks an Ubuntu phased update this host is not yet selected for:
+	// apt lists it as upgradable, but an upgrade defers it until the host's
+	// phase comes up. It is pending, not installable, so counts leave it out.
+	Phased bool `json:"phased,omitempty"`
 }
 
 type ReportUpdatesRequest struct {
diff --git a/proto/vantage/v1/vantage.proto b/proto/vantage/v1/vantage.proto
index b21f7b1..a7a8da1 100644
--- a/proto/vantage/v1/vantage.proto
+++ b/proto/vantage/v1/vantage.proto
@@ -127,6 +127,7 @@ message PackageUpdate {
   string name            = 1;
   string current_version = 2;
   string new_version     = 3;
+  bool   phased          = 4; // Ubuntu phased update this host is not yet selected for; deferred by apt
 }
 
 message ReportUpdatesRequest {