diff --git a/.changeset/prepare-specialized-app-signin-flow.md b/.changeset/prepare-specialized-app-signin-flow.md
index be7ddca934..1ee2dba443 100644
--- a/.changeset/prepare-specialized-app-signin-flow.md
+++ b/.changeset/prepare-specialized-app-signin-flow.md
@@ -3,4 +3,4 @@
 '@backstage/frontend-defaults': patch
 ---
 
-Adds `prepareSpecializedApp` as a new two-phase app wiring API for rendering a bootstrap tree before full app finalization. The bootstrap phase is now exposed as a partial app tree that consumers can render while subscribing to phase transitions, while the opaque reusable `sessionState` is stored internally on the prepared app and returned from `getFinalizedApp()` and `finalize()`. That session state can also be passed into a future `prepareSpecializedApp` call to skip sign-in and reuse the prepared session. The existing `createSpecializedApp` API is now deprecated and backed by `prepareSpecializedApp().finalize()`, while `createApp` has been updated to use the same prepare/finalize flow.
+Adds `prepareSpecializedApp` as a new two-phase app wiring API for rendering a bootstrap tree before full app finalization. The bootstrap phase is exposed as a partial app tree through `getBootstrapApp()`, while `onFinalized()` provides a one-way handoff to the finalized app once bootstrap completes. The opaque reusable `sessionState` is returned from the finalized app and can be passed into a future `prepareSpecializedApp` call to skip sign-in and reuse the prepared session. The existing `createSpecializedApp` API is now deprecated and backed by `prepareSpecializedApp().finalize()`, while `createApp` has been updated to use the same prepare/finalize flow.
diff --git a/packages/frontend-defaults/src/createApp.tsx b/packages/frontend-defaults/src/createApp.tsx
index 41c70adcf5..061137071b 100644
--- a/packages/frontend-defaults/src/createApp.tsx
+++ b/packages/frontend-defaults/src/createApp.tsx
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { JSX, lazy, ReactNode, Suspense, useSyncExternalStore } from 'react';
+import { JSX, lazy, ReactNode, Suspense, useEffect, useState } from 'react';
 import {
   ConfigApi,
   coreExtensionData,
@@ -150,11 +150,14 @@ function PreparedAppRoot(props: {
   preparedApp: PreparedSpecializedApp;
 }): JSX.Element {
   const bootstrapApp = props.preparedApp.getBootstrapApp();
-  const finalizedApp: FinalizedSpecializedApp | undefined =
-    useSyncExternalStore(
-      props.preparedApp.subscribe,
-      props.preparedApp.getFinalizedApp,
-    );
+  const [finalizedApp, setFinalizedApp] = useState<
+    FinalizedSpecializedApp | undefined
+  >();
+
+  useEffect(
+    () => props.preparedApp.onFinalized(setFinalizedApp),
+    [props.preparedApp],
+  );
 
   if (!finalizedApp) {
     return bootstrapApp.tree.root.instance!.getData(