diff --git a/keyserver/src/endpoints.js b/keyserver/src/endpoints.js
--- a/keyserver/src/endpoints.js
+++ b/keyserver/src/endpoints.js
@@ -7,6 +7,7 @@
 import type { PolicyType } from 'lib/facts/policies.js';
 import type { Endpoint } from 'lib/types/endpoints.js';
 import { calendarQueryValidator } from 'lib/types/entry-types.js';
+import { sessionStateValidator } from 'lib/types/session-types.js';
 import { endpointValidators } from 'lib/types/validators/endpoint-validators.js';
 import { updateUserAvatarRequestValidator } from 'lib/utils/avatar-utils.js';
 
@@ -121,6 +122,7 @@
   roleDeletionRequestInputValidator,
   roleModificationRequestInputValidator,
 } from './responders/thread-responders.js';
+import { fetchPendingUpdatesResponder } from './responders/update-responders.js';
 import {
   keyserverAuthRequestInputValidator,
   keyserverAuthResponder,
@@ -289,6 +291,11 @@
     inputValidator: fetchMessageInfosRequestInputValidator,
     policies: baseLegalPolicies,
   },
+  fetch_pending_updates: {
+    responder: fetchPendingUpdatesResponder,
+    inputValidator: sessionStateValidator,
+    policies: baseLegalPolicies,
+  },
   fetch_pinned_messages: {
     responder: fetchPinnedMessagesResponder,
     inputValidator: fetchPinnedMessagesResponderInputValidator,
diff --git a/keyserver/src/responders/update-responders.js b/keyserver/src/responders/update-responders.js
new file mode 100644
--- /dev/null
+++ b/keyserver/src/responders/update-responders.js
@@ -0,0 +1,16 @@
+// @flow
+
+import type { SessionState } from 'lib/types/session-types.js';
+import type { ServerStateSyncSocketPayload } from 'lib/types/socket-types.js';
+
+import { Viewer } from '../session/viewer.js';
+import { fetchDataForSocketInit } from '../socket/fetch-data.js';
+
+function fetchPendingUpdatesResponder(
+  viewer: Viewer,
+  request: SessionState,
+): Promise<ServerStateSyncSocketPayload> {
+  return fetchDataForSocketInit(viewer, request);
+}
+
+export { fetchPendingUpdatesResponder };
diff --git a/lib/types/endpoints.js b/lib/types/endpoints.js
--- a/lib/types/endpoints.js
+++ b/lib/types/endpoints.js
@@ -39,15 +39,16 @@
 });
 type UploadEndpoint = $Values<typeof uploadEndpoints>;
 
-const intialReduxStateEndpoints = Object.freeze({
+const largeDataFetchEndpoints = Object.freeze({
   GET_INITIAL_REDUX_STATE: 'get_initial_redux_state',
+  FETCH_PENDING_UPDATES: 'fetch_pending_updates',
 });
-type InitialReduxStateEndpoint = $Values<typeof intialReduxStateEndpoints>;
+type LargeDataFetchEndpoint = $Values<typeof largeDataFetchEndpoints>;
 
 type HTTPOnlyEndpoint =
   | SessionChangingEndpoint
   | UploadEndpoint
-  | InitialReduxStateEndpoint;
+  | LargeDataFetchEndpoint;
 
 const socketOnlyEndpoints = Object.freeze({
   UPDATE_ACTIVITY: 'update_activity',
diff --git a/lib/types/socket-types.js b/lib/types/socket-types.js
--- a/lib/types/socket-types.js
+++ b/lib/types/socket-types.js
@@ -294,10 +294,11 @@
 export type ServerStateSyncSocketPayload =
   | ServerStateSyncFullSocketPayload
   | ServerStateSyncIncrementalSocketPayload;
-const serverStateSyncSocketPayloadValidator = t.union([
-  serverStateSyncFullSocketPayloadValidator,
-  serverStateSyncIncrementalSocketPayloadValidator,
-]);
+export const serverStateSyncSocketPayloadValidator: TUnion<ServerStateSyncSocketPayload> =
+  t.union([
+    serverStateSyncFullSocketPayloadValidator,
+    serverStateSyncIncrementalSocketPayloadValidator,
+  ]);
 
 export type ServerStateSyncServerSocketMessage = {
   +type: 0,
diff --git a/lib/types/validators/endpoint-validators.js b/lib/types/validators/endpoint-validators.js
--- a/lib/types/validators/endpoint-validators.js
+++ b/lib/types/validators/endpoint-validators.js
@@ -62,6 +62,7 @@
 import { inviteLinkValidator } from '../link-types.js';
 import { uploadMultimediaResultValidator } from '../media-types.js';
 import { getOlmSessionInitializationDataResponseValidator } from '../request-types.js';
+import { serverStateSyncSocketPayloadValidator } from '../socket-types.js';
 
 const sessionChangingEndpoints = Object.freeze({
   log_out: {
@@ -93,10 +94,13 @@
   },
 });
 
-const initialReduxStateEndpoints = Object.freeze({
+const largeDataFetchEndpoints = Object.freeze({
   get_initial_redux_state: {
     validator: initialReduxStateValidator,
   },
+  fetch_pending_updates: {
+    validator: serverStateSyncSocketPayloadValidator,
+  },
 });
 
 const socketOnlyEndpoints = Object.freeze({
@@ -179,7 +183,7 @@
 export const endpointValidators = Object.freeze({
   ...sessionChangingEndpoints,
   ...uploadEndpoints,
-  ...initialReduxStateEndpoints,
+  ...largeDataFetchEndpoints,
   ...socketOnlyEndpoints,
   ...socketPreferredEndpoints,
   ...httpPreferredEndpoints,