diff --git a/lib/hooks/thread-search-hooks.js b/lib/hooks/thread-search-hooks.js
--- a/lib/hooks/thread-search-hooks.js
+++ b/lib/hooks/thread-search-hooks.js
@@ -2,6 +2,7 @@
 
 import * as React from 'react';
 
+import { useUsersSupportThickThreads } from './user-identities-hooks.js';
 import { searchUsers as searchUserCall } from '../actions/user-actions.js';
 import { useLegacyAshoatKeyserverCall } from '../keyserver-conn/legacy-keyserver-call.js';
 import { useGlobalThreadSearchIndex } from '../selectors/nav-selectors.js';
@@ -14,9 +15,14 @@
 import { useSelector } from '../utils/redux-utils.js';
 import { usingCommServicesAccessToken } from '../utils/services-utils.js';
 
+export type UserSearchResult = $ReadOnly<{
+  ...GlobalAccountUserInfo,
+  +supportThickThreads: boolean,
+}>;
+
 type ThreadListSearchResult = {
   +threadSearchResults: $ReadOnlySet<string>,
-  +usersSearchResults: $ReadOnlyArray<GlobalAccountUserInfo>,
+  +usersSearchResults: $ReadOnlyArray<UserSearchResult>,
 };
 
 function useThreadListSearch(
@@ -27,7 +33,7 @@
   const forwardLookupSearchText = useForwardLookupSearchText(searchText);
 
   const filterAndSetUserResults = React.useCallback(
-    (userInfos: $ReadOnlyArray<GlobalAccountUserInfo>) => {
+    (userInfos: $ReadOnlyArray<UserSearchResult>) => {
       const usersResults = userInfos.filter(
         info => !usersWithPersonalThread.has(info.id) && info.id !== viewerID,
       );
@@ -45,7 +51,12 @@
       }
 
       const { userInfos } = await legacyCallSearchUsers(usernamePrefix);
-      filterAndSetUserResults(userInfos);
+      filterAndSetUserResults(
+        userInfos.map(userInfo => ({
+          ...userInfo,
+          supportThickThreads: false,
+        })),
+      );
     },
     [filterAndSetUserResults, legacyCallSearchUsers],
   );
@@ -54,7 +65,7 @@
     new Set<string>(),
   );
   const [usersSearchResults, setUsersSearchResults] = React.useState<
-    $ReadOnlyArray<GlobalAccountUserInfo>,
+    $ReadOnlyArray<UserSearchResult>,
   >([]);
   const threadSearchIndex = useGlobalThreadSearchIndex();
   React.useEffect(() => {
@@ -72,12 +83,25 @@
     legacySearchUsers,
   ]);
 
+  const usersSupportThickThreads = useUsersSupportThickThreads();
   const identitySearchUsers = useSearchUsers(forwardLookupSearchText);
   React.useEffect(() => {
-    if (usingCommServicesAccessToken) {
-      filterAndSetUserResults(identitySearchUsers);
-    }
-  }, [filterAndSetUserResults, identitySearchUsers]);
+    void (async () => {
+      if (!usingCommServicesAccessToken) {
+        return;
+      }
+
+      const userIDsSupportingThickThreads = await usersSupportThickThreads(
+        identitySearchUsers.map(user => user.id),
+      );
+      filterAndSetUserResults(
+        identitySearchUsers.map(search => ({
+          ...search,
+          supportThickThreads: userIDsSupportingThickThreads.has(search.id),
+        })),
+      );
+    })();
+  }, [filterAndSetUserResults, identitySearchUsers, usersSupportThickThreads]);
 
   return { threadSearchResults, usersSearchResults };
 }
diff --git a/lib/hooks/user-identities-hooks.js b/lib/hooks/user-identities-hooks.js
new file mode 100644
--- /dev/null
+++ b/lib/hooks/user-identities-hooks.js
@@ -0,0 +1,47 @@
+// @flow
+
+import * as React from 'react';
+
+import { useAllowOlmViaTunnelbrokerForDMs } from './flag-hooks.js';
+import { useFindUserIdentities } from '../actions/find-user-identities-actions.js';
+import { userHasDeviceList } from '../shared/thread-utils.js';
+import { useSelector } from '../utils/redux-utils.js';
+
+function useUsersSupportThickThreads(): (
+  userIDs: $ReadOnlyArray<string>,
+) => Promise<$ReadOnlySet<string>> {
+  const findUserIdentities = useFindUserIdentities();
+  const auxUserInfos = useSelector(state => state.auxUserStore.auxUserInfos);
+  const allowOlmViaTunnelbrokerForDMs = useAllowOlmViaTunnelbrokerForDMs();
+
+  return React.useCallback(
+    async (userIDs: $ReadOnlyArray<string>) => {
+      const usersSupportingThickThreads = new Set<string>();
+
+      if (!allowOlmViaTunnelbrokerForDMs) {
+        return usersSupportingThickThreads;
+      }
+
+      const usersNeedingFetch = [];
+      for (const userID of userIDs) {
+        if (userHasDeviceList(userID, auxUserInfos)) {
+          usersSupportingThickThreads.add(userID);
+        } else {
+          usersNeedingFetch.push(userID);
+        }
+      }
+      if (usersNeedingFetch.length > 0) {
+        const { identities } = await findUserIdentities(usersNeedingFetch);
+        for (const userID of usersNeedingFetch) {
+          if (identities[userID]) {
+            usersSupportingThickThreads.add(userID);
+          }
+        }
+      }
+      return usersSupportingThickThreads;
+    },
+    [allowOlmViaTunnelbrokerForDMs, auxUserInfos, findUserIdentities],
+  );
+}
+
+export { useUsersSupportThickThreads };
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
@@ -16,6 +16,8 @@
 import genesis from '../facts/genesis.js';
 import { useLoggedInUserInfo } from '../hooks/account-hooks.js';
 import { useAllowOlmViaTunnelbrokerForDMs } from '../hooks/flag-hooks.js';
+import { type UserSearchResult } from '../hooks/thread-search-hooks.js';
+import { useUsersSupportThickThreads } from '../hooks/user-identities-hooks.js';
 import { extractKeyserverIDFromIDOptional } from '../keyserver-conn/keyserver-call-utils.js';
 import {
   hasPermission,
@@ -95,7 +97,6 @@
 import { updateTypes } from '../types/update-types-enum.js';
 import { type ClientUpdateInfo } from '../types/update-types.js';
 import type {
-  GlobalAccountUserInfo,
   UserInfos,
   AccountUserInfo,
   LoggedInUserInfo,
@@ -604,14 +605,14 @@
   loggedInUserInfo: LoggedInUserInfo,
   userID: string,
   username: ?string,
-  allowOlmViaTunnelbrokerForDMs: boolean,
+  supportThickThreads: boolean,
 ): PendingPersonalThread {
   const pendingPersonalThreadUserInfo = {
     id: userID,
     username: username,
   };
 
-  const threadType = allowOlmViaTunnelbrokerForDMs
+  const threadType = supportThickThreads
     ? threadTypes.PERSONAL
     : threadTypes.GENESIS_PERSONAL;
 
@@ -627,14 +628,14 @@
 function createPendingThreadItem(
   loggedInUserInfo: LoggedInUserInfo,
   user: UserIDAndUsername,
-  allowOlmViaTunnelbrokerForDMs: boolean,
+  supportThickThreads: boolean,
 ): ChatThreadItem {
   const { threadInfo, pendingPersonalThreadUserInfo } =
     createPendingPersonalThread(
       loggedInUserInfo,
       user.id,
       user.username,
-      allowOlmViaTunnelbrokerForDMs,
+      supportThickThreads,
     );
 
   return {
@@ -1440,9 +1441,8 @@
   searchText: string,
   threadFilter: ThreadInfo => boolean,
   threadSearchResults: $ReadOnlySet<string>,
-  usersSearchResults: $ReadOnlyArray<GlobalAccountUserInfo>,
+  usersSearchResults: $ReadOnlyArray<UserSearchResult>,
   loggedInUserInfo: ?LoggedInUserInfo,
-  allowOlmViaTunnelbrokerForDMs: boolean,
 ): $ReadOnlyArray<ChatThreadItem> {
   if (!searchText) {
     return chatListData.filter(
@@ -1478,7 +1478,7 @@
         createPendingThreadItem(
           loggedInUserInfo,
           user,
-          allowOlmViaTunnelbrokerForDMs,
+          user.supportThickThreads,
         ),
       ),
     );
@@ -1712,7 +1712,19 @@
 
   const usersWithPersonalThread = useSelector(usersWithPersonalThreadSelector);
 
-  const allowOlmViaTunnelbrokerForDMs = useAllowOlmViaTunnelbrokerForDMs();
+  const [supportThickThreads, setSupportThickThreads] = React.useState(false);
+  const usersSupportThickThreads = useUsersSupportThickThreads();
+
+  React.useEffect(() => {
+    void (async () => {
+      if (!userInfo) {
+        setSupportThickThreads(false);
+        return;
+      }
+      const result = await usersSupportThickThreads([userInfo.id]);
+      setSupportThickThreads(result.has(userInfo.id));
+    })();
+  }, [userInfo, usersSupportThickThreads]);
 
   return React.useMemo(() => {
     if (!loggedInUserInfo || !userID || !username) {
@@ -1738,16 +1750,16 @@
       loggedInUserInfo,
       userID,
       username,
-      allowOlmViaTunnelbrokerForDMs,
+      supportThickThreads,
     );
 
     return pendingPersonalThreadInfo;
   }, [
-    allowOlmViaTunnelbrokerForDMs,
     isViewerProfile,
     loggedInUserInfo,
     personalThreadInfos,
     privateThreadInfos,
+    supportThickThreads,
     userID,
     username,
     usersWithPersonalThread,
diff --git a/native/chat/chat-thread-list.react.js b/native/chat/chat-thread-list.react.js
--- a/native/chat/chat-thread-list.react.js
+++ b/native/chat/chat-thread-list.react.js
@@ -279,8 +279,6 @@
     ],
   );
 
-  const allowOlmViaTunnelbrokerForDMs = useAllowOlmViaTunnelbrokerForDMs();
-
   const listData: $ReadOnlyArray<Item> = React.useMemo(() => {
     const chatThreadItems = getThreadListSearchResults(
       boundChatListData,
@@ -289,7 +287,6 @@
       threadSearchResults,
       usersSearchResults,
       loggedInUserInfo,
-      allowOlmViaTunnelbrokerForDMs,
     );
 
     const chatItems: Item[] = [...chatThreadItems];
@@ -304,7 +301,6 @@
 
     return chatItems;
   }, [
-    allowOlmViaTunnelbrokerForDMs,
     boundChatListData,
     emptyItem,
     filterThreads,
diff --git a/web/chat/thread-list-provider.js b/web/chat/thread-list-provider.js
--- a/web/chat/thread-list-provider.js
+++ b/web/chat/thread-list-provider.js
@@ -4,7 +4,6 @@
 import * as React from 'react';
 
 import { useLoggedInUserInfo } from 'lib/hooks/account-hooks.js';
-import { useAllowOlmViaTunnelbrokerForDMs } from 'lib/hooks/flag-hooks.js';
 import { useThreadListSearch } from 'lib/hooks/thread-search-hooks.js';
 import {
   type ChatThreadItem,
@@ -180,7 +179,6 @@
   );
   const threadFilter =
     activeTab === 'Muted' ? threadInBackgroundChatList : threadInHomeChatList;
-  const allowOlmViaTunnelbrokerForDMs = useAllowOlmViaTunnelbrokerForDMs();
   const chatListDataWithoutFilter = getThreadListSearchResults(
     chatListData,
     searchText,
@@ -188,7 +186,6 @@
     threadSearchResults,
     usersSearchResults,
     loggedInUserInfo,
-    allowOlmViaTunnelbrokerForDMs,
   );
   const activeTopLevelChatThreadItem = useChatThreadItem(
     activeTopLevelThreadInfo,