diff --git a/shared/tunnelbroker_messages/src/messages/connection_initialization_response.rs b/shared/tunnelbroker_messages/src/messages/connection_initialization_response.rs
new file mode 100644
--- /dev/null
+++ b/shared/tunnelbroker_messages/src/messages/connection_initialization_response.rs
@@ -0,0 +1,56 @@
+//! Message sent from Tunnelbroker to WebSocket as a response to
+//! ConnectionInitializationMessage.
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+#[serde(tag = "type", content = "data")]
+pub enum ConnectionInitializationStatus {
+  Success,
+  Error(String),
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Debug)]
+#[serde(tag = "type", rename_all = "camelCase")]
+pub struct ConnectionInitializationResponse {
+  pub status: ConnectionInitializationStatus,
+}
+
+#[cfg(test)]
+mod connection_init_response_tests {
+  use super::*;
+
+  #[test]
+  fn test_connection_init_response_success() {
+    let example_payload = r#"{
+          "type":"ConnectionInitializationResponse",
+          "status": {"type":"Success"}
+        }"#;
+
+    let request =
+      serde_json::from_str::<ConnectionInitializationResponse>(example_payload)
+        .unwrap();
+
+    assert_eq!(request.status, ConnectionInitializationStatus::Success);
+  }
+
+  #[test]
+  fn test_connection_init_response_error() {
+    let example_payload = r#"{
+          "type": "ConnectionInitializationResponse",
+          "status": {
+            "type":"Error",
+            "data":"Something went wrong"
+          }
+        }"#;
+
+    let request =
+      serde_json::from_str::<ConnectionInitializationResponse>(example_payload)
+        .unwrap();
+
+    assert_eq!(
+      request.status,
+      ConnectionInitializationStatus::Error("Something went wrong".into())
+    );
+  }
+}
diff --git a/shared/tunnelbroker_messages/src/messages/mod.rs b/shared/tunnelbroker_messages/src/messages/mod.rs
--- a/shared/tunnelbroker_messages/src/messages/mod.rs
+++ b/shared/tunnelbroker_messages/src/messages/mod.rs
@@ -1,5 +1,6 @@
 //! Messages sent between Tunnelbroker and a device.
 
+pub mod connection_initialization_response;
 pub mod keys;
 pub mod message_receive_confirmation;
 pub mod message_to_device;
@@ -7,6 +8,7 @@
 pub mod message_to_device_request_status;
 pub mod session;
 
+pub use connection_initialization_response::*;
 pub use keys::*;
 pub use message_receive_confirmation::*;
 pub use message_to_device::*;
@@ -21,6 +23,7 @@
 pub enum Messages {
   RefreshKeysRequest(RefreshKeyRequest),
   ConnectionInitializationMessage(ConnectionInitializationMessage),
+  ConnectionInitializationResponse(ConnectionInitializationResponse),
   // MessageToDeviceRequestStatus must be placed before MessageToDeviceRequest.
   // This is due to serde's pattern matching behavior where it prioritizes
   // the first matching pattern it encounters.
diff --git a/shared/tunnelbroker_messages/src/messages/session.rs b/shared/tunnelbroker_messages/src/messages/session.rs
--- a/shared/tunnelbroker_messages/src/messages/session.rs
+++ b/shared/tunnelbroker_messages/src/messages/session.rs
@@ -43,11 +43,6 @@
   pub device_os: Option<String>,
 }
 
-#[derive(Serialize, Deserialize)]
-pub struct ConnectionInitializationResponse {
-  pub session_id: String,
-}
-
 #[cfg(test)]
 mod session_tests {
   use super::*;