diff --git a/lib/utils/conversion-utils.js b/lib/utils/conversion-utils.js
--- a/lib/utils/conversion-utils.js
+++ b/lib/utils/conversion-utils.js
@@ -4,7 +4,12 @@
 import _mapValues from 'lodash/fp/mapValues.js';
 import type { TInterface, TType } from 'tcomb';
 
+import { convertIDToNewSchema } from './migration-utils.js';
 import { assertWithValidator, tID } from './validation-utils.js';
+import {
+  getPendingThreadID,
+  parsePendingThreadID,
+} from '../shared/thread-utils.js';
 
 function convertServerIDsToClientIDs<T>(
   serverPrefixID: string,
@@ -16,7 +21,7 @@
       console.warn(`Server id '${id}' already has a prefix`);
       return id;
     }
-    return `${serverPrefixID}|${id}`;
+    return convertIDToNewSchema(id, serverPrefixID);
   };
 
   return convertObject(outputValidator, data, [tID], conversionFunction);
@@ -33,7 +38,20 @@
       return id.substr(prefix.length);
     }
 
-    throw new Error('invalid_client_id_prefix');
+    const pendingIDContents = parsePendingThreadID(id);
+    if (!pendingIDContents) {
+      throw new Error('invalid_client_id_prefix');
+    }
+
+    if (!pendingIDContents.sourceMessageID) {
+      return id;
+    }
+
+    return getPendingThreadID(
+      pendingIDContents.threadType,
+      pendingIDContents.memberIDs,
+      pendingIDContents.sourceMessageID.substr(prefix.length),
+    );
   };
 
   return convertObject(outputValidator, data, [tID], conversionFunction);
diff --git a/lib/utils/conversion-utils.test.js b/lib/utils/conversion-utils.test.js
--- a/lib/utils/conversion-utils.test.js
+++ b/lib/utils/conversion-utils.test.js
@@ -67,3 +67,18 @@
     }
   });
 });
+
+describe('Pending ids tests', () => {
+  it('should convert pending ids', () => {
+    const validator = t.list(tID);
+    const serverData = ['pending/sidebar/1', 'pending/type4/1+2+3'];
+    const clientData = ['pending/sidebar/0|1', 'pending/type4/1+2+3'];
+
+    expect(
+      convertServerIDsToClientIDs('0', validator, serverData),
+    ).toStrictEqual(clientData);
+    expect(
+      convertClientIDsToServerIDs('0', validator, clientData),
+    ).toStrictEqual(serverData);
+  });
+});
diff --git a/web/redux/initial-state-gate.js b/web/redux/initial-state-gate.js
--- a/web/redux/initial-state-gate.js
+++ b/web/redux/initial-state-gate.js
@@ -6,7 +6,9 @@
 import type { Persistor } from 'redux-persist/es/types';
 
 import { useServerCall } from 'lib/utils/action-utils.js';
+import { convertIDToNewSchema } from 'lib/utils/migration-utils.js';
 import { infoFromURL } from 'lib/utils/url-utils.js';
+import { ashoatKeyserverID } from 'lib/utils/validation-utils.js';
 
 import { getInitialReduxState, setInitialReduxState } from './action-types.js';
 import { useSelector } from './redux-utils.js';
@@ -35,7 +37,14 @@
       prevIsRehydrated.current = isRehydrated;
       (async () => {
         try {
-          const urlInfo = infoFromURL(decodeURI(window.location.href));
+          let urlInfo = infoFromURL(decodeURI(window.location.href));
+          // Handle older links
+          if (urlInfo.thread) {
+            urlInfo = {
+              ...urlInfo,
+              thread: convertIDToNewSchema(urlInfo.thread, ashoatKeyserverID),
+            };
+          }
           const payload = await callGetInitialReduxState(urlInfo);
           dispatch({ type: setInitialReduxState, payload });
         } catch (err) {