diff --git a/keyserver/src/endpoints.js b/keyserver/src/endpoints.js
--- a/keyserver/src/endpoints.js
+++ b/keyserver/src/endpoints.js
@@ -18,7 +18,10 @@
   calendarQueryUpdateResponder,
 } from './responders/entry-responders.js';
 import type { JSONResponder } from './responders/handlers.js';
-import { getSessionPublicKeysResponder } from './responders/keys-responders.js';
+import {
+  getSessionPublicKeysResponder,
+  getOlmSessionInitializationDataResponder,
+} from './responders/keys-responders.js';
 import { messageReportCreationResponder } from './responders/message-report-responder.js';
 import {
   textMessageCreationResponder,
@@ -262,6 +265,10 @@
     responder: updateUserAvatarResponder,
     requiredPolicies: baseLegalPolicies,
   },
+  get_olm_session_initialization_data: {
+    responder: getOlmSessionInitializationDataResponder,
+    requiredPolicies: [],
+  },
 };
 
 export { jsonEndpoints };
diff --git a/keyserver/src/responders/keys-responders.js b/keyserver/src/responders/keys-responders.js
--- a/keyserver/src/responders/keys-responders.js
+++ b/keyserver/src/responders/keys-responders.js
@@ -2,12 +2,19 @@
 
 import t from 'tcomb';
 
-import type { GetSessionPublicKeysArgs } from 'lib/types/request-types.js';
+import type {
+  GetOlmSessionInitializationDataResponse,
+  GetOlmSessionInitializationDataRequest,
+  GetSessionPublicKeysArgs,
+} from 'lib/types/request-types.js';
 import type { SessionPublicKeys } from 'lib/types/session-types.js';
 import { tShape } from 'lib/utils/validation-utils.js';
 
 import { fetchSessionPublicKeys } from '../fetchers/key-fetchers.js';
+import { fetchKeyserverOlmAccount } from '../fetchers/olm-account-fetcher.js';
 import type { Viewer } from '../session/viewer.js';
+import { updateOlmAccount } from '../updaters/olm-account-updater.js';
+import { validateAccountPrekey } from '../utils/olm-utils.js';
 import { validateInput } from '../utils/validation-utils.js';
 
 const getSessionPublicKeysInputValidator = tShape({
@@ -26,4 +33,46 @@
   return await fetchSessionPublicKeys(request.session);
 }
 
-export { getSessionPublicKeysResponder };
+const getOlmSessionInitializationDataRequestInputValidator = tShape({
+  olmSessionType: t.enums.of(['primary', 'notifications']),
+  oneTimeKeysCount: t.Number,
+});
+
+async function getOlmSessionInitializationDataResponder(
+  viewer: Viewer,
+  input: any,
+): Promise<GetOlmSessionInitializationDataResponse> {
+  await validateInput(
+    viewer,
+    getOlmSessionInitializationDataRequestInputValidator,
+    input,
+  );
+  const request: GetOlmSessionInitializationDataRequest = input;
+
+  const { account, picklingKey } = await fetchKeyserverOlmAccount(
+    input.olmSessionType,
+  );
+
+  await validateAccountPrekey(account);
+  const prekey = account.prekey();
+
+  account.generate_one_time_keys(request.oneTimeKeysCount);
+  const oneTimeKeys = account.one_time_keys();
+  account.mark_keys_as_published();
+
+  const identityKeys = account.identity_keys();
+
+  const isPrimary = request.olmSessionType === 'primary';
+  await updateOlmAccount(account, picklingKey, isPrimary);
+
+  return {
+    identityKeys,
+    prekey,
+    oneTimeKeys,
+  };
+}
+
+export {
+  getSessionPublicKeysResponder,
+  getOlmSessionInitializationDataResponder,
+};
diff --git a/lib/actions/user-actions.js b/lib/actions/user-actions.js
--- a/lib/actions/user-actions.js
+++ b/lib/actions/user-actions.js
@@ -14,7 +14,11 @@
   ClientAvatar,
   UpdateUserAvatarRequest,
 } from '../types/avatar-types.js';
-import type { GetSessionPublicKeysArgs } from '../types/request-types.js';
+import type {
+  GetSessionPublicKeysArgs,
+  GetOlmSessionInitializationDataRequest,
+  GetOlmSessionInitializationDataResponse,
+} from '../types/request-types.js';
 import type { UserSearchResult } from '../types/search-types.js';
 import type {
   SessionPublicKeys,
@@ -235,6 +239,19 @@
     return await callServerEndpoint('get_session_public_keys', data);
   };
 
+const getOlmSessionInitializationData =
+  (
+    callServerEndpoint: CallServerEndpoint,
+  ): ((
+    data: GetOlmSessionInitializationDataRequest,
+  ) => Promise<GetOlmSessionInitializationDataResponse>) =>
+  async data => {
+    return await callServerEndpoint(
+      'get_olm_session_initialization_data',
+      data,
+    );
+  };
+
 const policyAcknowledgmentActionTypes = Object.freeze({
   started: 'POLICY_ACKNOWLEDGMENT_STARTED',
   success: 'POLICY_ACKNOWLEDGMENT_SUCCESS',
@@ -267,6 +284,7 @@
   deleteAccount,
   deleteAccountActionTypes,
   getSessionPublicKeys,
+  getOlmSessionInitializationData,
   mergeUserInfos,
   logIn,
   logInActionTypes,
diff --git a/lib/types/endpoints.js b/lib/types/endpoints.js
--- a/lib/types/endpoints.js
+++ b/lib/types/endpoints.js
@@ -87,6 +87,7 @@
   SIWE_NONCE: 'siwe_nonce',
   SIWE_AUTH: 'siwe_auth',
   UPDATE_USER_AVATAR: 'update_user_avatar',
+  GET_OLM_SESSION_INITIALIZATION_DATA: 'get_olm_session_initialization_data',
 });
 type SocketPreferredEndpoint = $Values<typeof socketPreferredEndpoints>;
 
diff --git a/lib/types/request-types.js b/lib/types/request-types.js
--- a/lib/types/request-types.js
+++ b/lib/types/request-types.js
@@ -197,3 +197,14 @@
 export type GetSessionPublicKeysArgs = {
   +session: string,
 };
+
+export type GetOlmSessionInitializationDataRequest = {
+  +olmSessionType: 'primary' | 'notifications',
+  +oneTimeKeysCount: number,
+};
+
+export type GetOlmSessionInitializationDataResponse = {
+  +identityKeys: string,
+  +prekey: string,
+  +oneTimeKeys: string,
+};