diff --git a/lib/shared/sidebar-utils.js b/lib/shared/sidebar-utils.js
--- a/lib/shared/sidebar-utils.js
+++ b/lib/shared/sidebar-utils.js
@@ -102,11 +102,11 @@
     }
   }
 
+  const config = threadSpecs[parentThreadInfo.type].protocol().sidebarConfig;
+  invariant(config, `Thread type ${parentThreadInfo.type} can't have sidebars`);
   return createPendingThread({
     viewerID,
-    threadType:
-      threadSpecs[parentThreadInfo.type].protocol().sidebarConfig
-        .sidebarThreadType,
+    threadType: config.sidebarThreadType,
     members: [...initialMembers.values()],
     parentThreadInfo,
     threadColor: color,
diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -392,8 +392,9 @@
 ): string {
   let pendingThreadKey;
   if (sourceMessageID) {
-    const prefix =
-      threadSpecs[threadType].protocol().sidebarConfig.pendingSidebarURLPrefix;
+    const config = threadSpecs[threadType].protocol().sidebarConfig;
+    invariant(config, `Thread type ${threadType} doesn't support sidebars`);
+    const prefix = config.pendingSidebarURLPrefix;
     pendingThreadKey = `${prefix}/${sourceMessageID}`;
   } else {
     pendingThreadKey = [...memberIDs].sort().join('+');
@@ -421,8 +422,8 @@
   const [threadTypeString, threadKey] = pendingThreadIDMatches[1].split('/');
   const threadType =
     protocols().find(
-      p => p.sidebarConfig.pendingSidebarURLPrefix === threadTypeString,
-    )?.sidebarConfig.sidebarThreadType ??
+      p => p.sidebarConfig?.pendingSidebarURLPrefix === threadTypeString,
+    )?.sidebarConfig?.sidebarThreadType ??
     assertThreadType(Number(threadTypeString.replace('type', '')));
 
   const threadTypeStringIsSidebar = threadTypeIsSidebar(threadType);
@@ -1464,9 +1465,9 @@
     return threadInfo;
   }
   members.push(...mentionedNewMembers);
-  const threadType =
-    threadSpecs[parentThreadInfo.type].protocol().sidebarConfig
-      .sidebarThreadType;
+  const config = threadSpecs[parentThreadInfo.type].protocol().sidebarConfig;
+  invariant(config, `Thread type ${parentThreadInfo.type} can't have sidebars`);
+  const threadType = config.sidebarThreadType;
 
   return createPendingThread({
     viewerID,
diff --git a/lib/shared/threads/protocols/farcaster-thread-protocol.js b/lib/shared/threads/protocols/farcaster-thread-protocol.js
--- a/lib/shared/threads/protocols/farcaster-thread-protocol.js
+++ b/lib/shared/threads/protocols/farcaster-thread-protocol.js
@@ -17,15 +17,11 @@
 } from '../../../types/minimally-encoded-thread-permissions-types.js';
 import type { SubscriptionUpdateResult } from '../../../types/subscription-types.js';
 import type { ThreadType } from '../../../types/thread-types-enum.js';
-import { thickThreadTypes } from '../../../types/thread-types-enum.js';
 import type {
   ChangeThreadSettingsPayload,
   ThreadJoinPayload,
 } from '../../../types/thread-types.js';
-import {
-  farcasterThreadIDRegExp,
-  pendingThickSidebarURLPrefix,
-} from '../../../utils/validation-utils.js';
+import { farcasterThreadIDRegExp } from '../../../utils/validation-utils.js';
 import { messageNotifyTypes } from '../../messages/message-spec.js';
 import type { ThreadProtocol } from '../thread-spec.js';
 
@@ -149,13 +145,6 @@
 
   uploadMultimediaMetadataToKeyserver: false,
   canActionsTargetPendingMessages: false,
-
-  sidebarConfig: {
-    //TODO: Add this after ENG-10944
-    sidebarThreadType: thickThreadTypes.THICK_SIDEBAR,
-    pendingSidebarURLPrefix: pendingThickSidebarURLPrefix,
-  },
-
   messagesStoredOnServer: false,
   arePendingThreadsDescendantsOfGenesis: false,
   threadActivityUpdatedByDMActivityHandler: false,
diff --git a/lib/shared/threads/thread-spec.js b/lib/shared/threads/thread-spec.js
--- a/lib/shared/threads/thread-spec.js
+++ b/lib/shared/threads/thread-spec.js
@@ -389,7 +389,7 @@
   },
   +uploadMultimediaMetadataToKeyserver: boolean,
   +canActionsTargetPendingMessages: boolean,
-  +sidebarConfig: {
+  +sidebarConfig?: {
     +sidebarThreadType: ThreadType,
     +pendingSidebarURLPrefix: string,
   },