diff --git a/keyserver/src/responders/user-responders.js b/keyserver/src/responders/user-responders.js
--- a/keyserver/src/responders/user-responders.js
+++ b/keyserver/src/responders/user-responders.js
@@ -573,7 +573,7 @@
     );
   }
 
-  // 9. Try to double-write SIWE account info to the Identity service
+  // 9. Try to double-write SIWE account info to the Identity service.
   const userIDCopy = userID;
   if (identityKeys && signedIdentityKeysBlob) {
     const identityKeysCopy = identityKeys;
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
@@ -4,6 +4,7 @@
 
 import { type ActivityUpdate } from './activity-types.js';
 import type { Shape } from './core.js';
+import type { SignedIdentityKeysBlob } from './crypto-types.js';
 import type { Platform, PlatformDetails } from './device-types.js';
 import type { RawEntryInfo, CalendarQuery } from './entry-types.js';
 import type {
@@ -31,6 +32,7 @@
   CHECK_STATE: 6,
   INITIAL_ACTIVITY_UPDATES: 7,
   MORE_ONE_TIME_KEYS: 8,
+  SIGNED_IDENTITY_KEYS_BLOB: 9,
 });
 type ServerRequestType = $Values<typeof serverRequestTypes>;
 export function assertServerRequestType(
@@ -43,7 +45,8 @@
       serverRequestType === 5 ||
       serverRequestType === 6 ||
       serverRequestType === 7 ||
-      serverRequestType === 8,
+      serverRequestType === 8 ||
+      serverRequestType === 9,
     'number is not ServerRequestType enum',
   );
   return serverRequestType;
@@ -111,11 +114,20 @@
   +keys: $ReadOnlyArray<string>,
 };
 
+type SignedIdentityKeysBlobServerRequest = {
+  +type: 9,
+};
+type SignedIdentityKeysBlobClientResponse = {
+  +type: 9,
+  +signedIdentityKeysBlob: SignedIdentityKeysBlob,
+};
+
 export type ServerServerRequest =
   | PlatformServerRequest
   | PlatformDetailsServerRequest
   | ServerCheckStateServerRequest
-  | MoreOneTimeKeysServerRequest;
+  | MoreOneTimeKeysServerRequest
+  | SignedIdentityKeysBlobServerRequest;
 export type ClientResponse =
   | PlatformClientResponse
   | ThreadInconsistencyClientResponse
@@ -123,7 +135,8 @@
   | EntryInconsistencyClientResponse
   | CheckStateClientResponse
   | InitialActivityUpdatesClientResponse
-  | MoreOneTimeKeysClientResponse;
+  | MoreOneTimeKeysClientResponse
+  | SignedIdentityKeysBlobClientResponse;
 
 export type ClientCheckStateServerRequest = {
   +type: 6,
@@ -147,7 +160,8 @@
   | PlatformServerRequest
   | PlatformDetailsServerRequest
   | ClientCheckStateServerRequest
-  | MoreOneTimeKeysServerRequest;
+  | MoreOneTimeKeysServerRequest
+  | SignedIdentityKeysBlobServerRequest;
 
 // This is just the client variant of ClientResponse. The server needs to handle
 // multiple client versions so the type supports old versions of certain client
@@ -167,7 +181,8 @@
   | ClientEntryInconsistencyClientResponse
   | CheckStateClientResponse
   | InitialActivityUpdatesClientResponse
-  | MoreOneTimeKeysClientResponse;
+  | MoreOneTimeKeysClientResponse
+  | SignedIdentityKeysBlobClientResponse;
 
 export type ClientInconsistencyResponse =
   | ClientThreadInconsistencyClientResponse