diff --git a/src/actionTypes.js b/src/actionTypes.js
index 42e24253faa..8627b357de7 100644
--- a/src/actionTypes.js
+++ b/src/actionTypes.js
@@ -341,35 +341,42 @@ type EventMessageDeleteAction = {|
   type: typeof EVENT_MESSAGE_DELETE,
   messageIds: number[],
 |};
+
+// This is current to feature level 109:
+//   https://zulip.com/api/get-events#update_message
 type EventUpdateMessageAction = {|
   ...ServerEvent,
   type: typeof EVENT_UPDATE_MESSAGE,
-  edit_timestamp: number,
+  user_id: UserId,
+
+  // Any content changes apply to just message_id.
   message_id: number,
-  // TODO is it really right that just one of the orig_* is optional?
-  orig_content: string,
 
-  // TODO: The doc for this field isn't yet correct; it turns out that
-  // the question of whether `orig_subject` is present or not is
-  // complicated; see discussion at
-  // https://chat.zulip.org/#narrow/stream/206-zulip-terminal/topic/subject.20always.20present.20in.20event/near/1098954.
-  //
-  // We can be pretty sure of a few things, though:
-  // - it will not be present if the message doesn't have a topic
-  //   (i.e., if it's a private message)
-  // - it's guaranteed to be present if the topic did indeed change
-  // - it will never be an empty string, because the server doesn't
-  //   accept the empty string for a message's topic; it requires
-  //   clients to specify something like `(no topic)` if no topic is
-  //   desired.
+  // Any stream/topic changes apply to all of message_ids, which is
+  //   guaranteed to include message_id.
+  message_ids: $ReadOnlyArray<number>,
+
+  edit_timestamp: number,
+  stream_name?: string,
+  stream_id?: number,
+  new_stream_id?: number,
+  propagate_mode: 'change_one' | 'change_later' | 'change_all',
   orig_subject?: string,
+  subject: string,
+
+  // TODO(server-4.0): Changed in feat. 46 to array-of-objects shape, from string[]
+  topic_links?: $ReadOnlyArray<{| +text: string, +url: string |}> | $ReadOnlyArray<string>,
 
+  // TODO(server-3.0): Replaced in feat. 1 by topic_links
+  subject_links?: string[],
+
+  orig_content: string,
   orig_rendered_content: string,
   prev_rendered_content_version: number,
+  content: string,
   rendered_content: string,
-  subject_links: string[],
-  subject: string,
-  user_id: UserId,
+  is_me_message: boolean,
+  flags: $ReadOnlyArray<string>,
 |};
 
 type EventReactionCommon = {|
diff --git a/src/message/__tests__/messagesReducer-test.js b/src/message/__tests__/messagesReducer-test.js
index 9c483a3cb70..1095576ef37 100644
--- a/src/message/__tests__/messagesReducer-test.js
+++ b/src/message/__tests__/messagesReducer-test.js
@@ -175,13 +175,18 @@ describe('messagesReducer', () => {
         type: EVENT_UPDATE_MESSAGE,
         edit_timestamp: Date.now() - 1000,
         message_id: message3.id,
+        message_ids: [message3.id],
         orig_content: eg.randString(),
         orig_rendered_content: eg.randString(),
         prev_rendered_content_version: 0,
+        propagate_mode: 'change_one',
         rendered_content: eg.randString(),
+        content: eg.randString(),
         subject_links: [],
         subject: eg.randString(),
         user_id: message3.sender_id,
+        is_me_message: false,
+        flags: [],
       });
       const newState = messagesReducer(prevState, action);
       expect(newState).toBe(prevState);
@@ -211,13 +216,18 @@ describe('messagesReducer', () => {
         type: EVENT_UPDATE_MESSAGE,
         edit_timestamp: 123,
         message_id: message3New.id,
+        message_ids: [message3New.id],
         orig_content: '<p>Old content</p>',
         orig_rendered_content: '<p>Old content</p>',
         prev_rendered_content_version: 1,
+        propagate_mode: 'change_one',
         rendered_content: '<p>New content</p>',
+        content: 'New content',
         subject_links: [],
         subject: message3New.subject,
         user_id: message3New.sender_id,
+        is_me_message: false,
+        flags: [],
       });
       const expectedState = eg.makeMessagesState([message1, message2, message3New]);
       const newState = messagesReducer(prevState, action);
@@ -254,14 +264,19 @@ describe('messagesReducer', () => {
         type: EVENT_UPDATE_MESSAGE,
         edit_timestamp: 123,
         message_id: message1New.id,
+        message_ids: [message1New.id],
         orig_content: message1Old.content,
         orig_subject: message1Old.subject,
         orig_rendered_content: message1Old.content,
         prev_rendered_content_version: 1,
+        propagate_mode: 'change_one',
         rendered_content: message1New.content,
+        content: message1New.content,
         subject_links: [],
         subject: message1New.subject,
         user_id: message1Old.sender_id,
+        is_me_message: false,
+        flags: [],
       });
       const expectedState = eg.makeMessagesState([message1New]);
       const newState = messagesReducer(prevState, action);
@@ -307,14 +322,19 @@ describe('messagesReducer', () => {
         type: EVENT_UPDATE_MESSAGE,
         edit_timestamp: 456,
         message_id: message1Old.id,
+        message_ids: [message1Old.id],
         orig_content: message1Old.content,
         orig_rendered_content: message1Old.content,
         rendered_content: message1New.content,
+        content: message1New.content,
+        propagate_mode: 'change_one',
         subject: message1New.subject,
         orig_subject: message1Old.subject,
         prev_rendered_content_version: 1,
         user_id: message1New.sender_id,
         subject_links: [],
+        is_me_message: false,
+        flags: [],
       });
       const expectedState = eg.makeMessagesState([message1New]);
       const newState = messagesReducer(prevState, action);