diff --git a/models/instance.go b/models/instance.go
index 73435fe..ae52bab 100644
--- a/models/instance.go
+++ b/models/instance.go
@@ -31,4 +31,12 @@ type Instance struct {
 	LicenseBlob   string     `bson:"license_blob,omitempty" json:"-"`
 	LicenseTier   string     `bson:"license_tier,omitempty" json:"license_tier,omitempty"`
 	LicenseExpiry *time.Time `bson:"license_expiry,omitempty" json:"license_expiry,omitempty"`
+
+	// LockedAt and PurgeAfter are written by vantage-admin's cloudprov when the
+	// account that owns this instance is under a dispute. LockedAt makes the
+	// control plane refuse the instance everywhere; PurgeAfter, set only once a
+	// dispute has failed, authorises the reaper to delete it. Both absent is the
+	// normal state, and nothing but admin ever sets them.
+	LockedAt   *time.Time `bson:"locked_at,omitempty" json:"locked_at,omitempty"`
+	PurgeAfter *time.Time `bson:"purge_after,omitempty" json:"purge_after,omitempty"`
 }
diff --git a/models/instance_test.go b/models/instance_test.go
new file mode 100644
index 0000000..3da5ad2
--- /dev/null
+++ b/models/instance_test.go
@@ -0,0 +1,40 @@
+package models
+
+import (
+	"testing"
+	"time"
+
+	"go.mongodb.org/mongo-driver/v2/bson"
+)
+
+func TestInstanceLockFieldsBSON(t *testing.T) {
+	at := time.Date(2026, 9, 10, 10, 0, 0, 0, time.UTC)
+
+	raw, err := bson.Marshal(Instance{InstanceID: "i1", LockedAt: &at, PurgeAfter: &at})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	var set bson.M
+	if err := bson.Unmarshal(raw, &set); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	for _, k := range []string{"locked_at", "purge_after"} {
+		if _, ok := set[k]; !ok {
+			t.Errorf("%s missing from %v", k, set)
+		}
+	}
+
+	raw, err = bson.Marshal(Instance{InstanceID: "i1"})
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	var unset bson.M
+	if err := bson.Unmarshal(raw, &unset); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	for _, k := range []string{"locked_at", "purge_after"} {
+		if _, ok := unset[k]; ok {
+			t.Errorf("%s written for an unlocked instance: %v", k, unset)
+		}
+	}
+}