diff --git a/crates/wzp-proto/src/packet.rs b/crates/wzp-proto/src/packet.rs
index 7e106b0..bf4bd14 100644
--- a/crates/wzp-proto/src/packet.rs
+++ b/crates/wzp-proto/src/packet.rs
@@ -716,6 +716,9 @@ pub enum SignalMessage {
         success: bool,
         #[serde(skip_serializing_if = "Option::is_none")]
         error: Option<String>,
+        /// Relay's build version (git short hash).
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        relay_build: Option<String>,
     },
 
     /// Direct call offer routed through the relay to a specific peer.
diff --git a/crates/wzp-relay/src/main.rs b/crates/wzp-relay/src/main.rs
index 32abc52..121d350 100644
--- a/crates/wzp-relay/src/main.rs
+++ b/crates/wzp-relay/src/main.rs
@@ -1006,6 +1006,7 @@ async fn main() -> anyhow::Result<()> {
                 let _ = transport.send_signal(&SignalMessage::RegisterPresenceAck {
                     success: true,
                     error: None,
+                    relay_build: Some(BUILD_GIT_HASH.to_string()),
                 }).await;
 
                 info!(%addr, fingerprint = %client_fp, alias = ?client_alias, "signal client registered");
diff --git a/crates/wzp-relay/tests/multi_reflect.rs b/crates/wzp-relay/tests/multi_reflect.rs
index 49f0691..1d92102 100644
--- a/crates/wzp-relay/tests/multi_reflect.rs
+++ b/crates/wzp-relay/tests/multi_reflect.rs
@@ -65,6 +65,7 @@ async fn spawn_mock_relay() -> (SocketAddr, tokio::task::JoinHandle<()>) {
                                 .send_signal(&SignalMessage::RegisterPresenceAck {
                                     success: true,
                                     error: None,
+                                    relay_build: None,
                                 })
                                 .await;
                         }
diff --git a/desktop/src-tauri/src/lib.rs b/desktop/src-tauri/src/lib.rs
index 911f793..4b2c86d 100644
--- a/desktop/src-tauri/src/lib.rs
+++ b/desktop/src-tauri/src/lib.rs
@@ -966,8 +966,10 @@ fn do_register_signal(
     emit_call_debug(&app, "register_signal:register_presence_sent", serde_json::json!({}));
 
     match transport.recv_signal().await.map_err(|e| format!("{e}"))? {
-        Some(SignalMessage::RegisterPresenceAck { success: true, .. }) => {
-            emit_call_debug(&app, "register_signal:ack_received", serde_json::json!({}));
+        Some(SignalMessage::RegisterPresenceAck { success: true, relay_build, .. }) => {
+            emit_call_debug(&app, "register_signal:ack_received", serde_json::json!({
+                "relay_build": relay_build,
+            }));
         }
         _ => {
             emit_call_debug(&app, "register_signal:ack_failed", serde_json::json!({}));