diff --git a/lib/shared/messages/create-sidebar-message-spec.js b/lib/shared/messages/create-sidebar-message-spec.js
--- a/lib/shared/messages/create-sidebar-message-spec.js
+++ b/lib/shared/messages/create-sidebar-message-spec.js
@@ -7,6 +7,7 @@
   type CreateMessageInfoParams,
   type MessageSpec,
 } from './message-spec.js';
+import { joinResult } from './utils.js';
 import type { PlatformDetails } from '../../types/device-types.js';
 import { messageTypes } from '../../types/message-types.js';
 import type {
@@ -207,6 +208,10 @@
     };
   },
 
+  notificationCollapseKey(rawMessageInfo: RawCreateSidebarMessageInfo): string {
+    return joinResult(messageTypes.CREATE_SIDEBAR, rawMessageInfo.threadID);
+  },
+
   generatesNotifs: async () => pushTypes.NOTIF,
 
   userIDs(rawMessageInfo: RawCreateSidebarMessageInfo): $ReadOnlyArray<string> {
diff --git a/lib/shared/messages/sidebar-source-message-spec.js b/lib/shared/messages/sidebar-source-message-spec.js
--- a/lib/shared/messages/sidebar-source-message-spec.js
+++ b/lib/shared/messages/sidebar-source-message-spec.js
@@ -2,13 +2,14 @@
 
 import invariant from 'invariant';
 
-import type {
-  CreateMessageInfoParams,
-  MessageSpec,
-  NotificationTextsParams,
-  RawMessageInfoFromServerDBRowParams,
+import {
+  pushTypes,
+  type CreateMessageInfoParams,
+  type MessageSpec,
+  type NotificationTextsParams,
+  type RawMessageInfoFromServerDBRowParams,
 } from './message-spec.js';
-import { assertSingleMessageInfo } from './utils.js';
+import { assertSingleMessageInfo, joinResult } from './utils.js';
 import type { PlatformDetails } from '../../types/device-types.js';
 import type {
   MessageInfo,
@@ -177,7 +178,11 @@
     return await params.notificationTexts([sourceMessageInfo], threadInfo);
   },
 
-  generatesNotifs: async () => undefined,
+  notificationCollapseKey(rawMessageInfo: RawSidebarSourceMessageInfo): string {
+    return joinResult(messageTypes.CREATE_SIDEBAR, rawMessageInfo.threadID);
+  },
+
+  generatesNotifs: async () => pushTypes.NOTIF,
 
   startsThread: true,
 });