diff --git a/service/gcs/bridge/bridge.go b/service/gcs/bridge/bridge.go
index <HASH>..<HASH> 100644
--- a/service/gcs/bridge/bridge.go
+++ b/service/gcs/bridge/bridge.go
@@ -41,6 +41,9 @@ var capabilities = prot.GcsCapabilities{
 		},
 	},
 	RuntimeOsType: prot.OsTypeLinux,
+	GuestDefinedCapabilities: prot.GcsGuestCapabilities{
+		SignalProcessSupported: true,
+	},
 }
 
 // UnknownMessage represents the default handler logic for an unmatched request
diff --git a/service/gcs/prot/protocol.go b/service/gcs/prot/protocol.go
index <HASH>..<HASH> 100644
--- a/service/gcs/prot/protocol.go
+++ b/service/gcs/prot/protocol.go
@@ -249,7 +249,14 @@ type GcsCapabilities struct {
 	// GuestDefinedCapabilities define any JSON object that will be directly
 	// passed to a client of the HCS. This can be useful to pass runtime
 	// specific capabilities not tied to the platform itself.
-	GuestDefinedCapabilities interface{} `json:",omitempty"`
+	GuestDefinedCapabilities GcsGuestCapabilities `json:",omitempty"`
+}
+
+// GcsGuestCapabilities represents the customized guest capabilities supported
+// by this GCS.
+type GcsGuestCapabilities struct {
+	NamespaceAddRequestSupported bool `json:",omitempty"`
+	SignalProcessSupported       bool `json:",omitempty"`
 }
 
 // MessageBase is the base type embedded in all messages sent from the HCS to
Return GuestDefinedCapabilities with SignalProcess support