diff --git a/keyserver/src/responders/message-responders.js b/keyserver/src/responders/message-responders.js
--- a/keyserver/src/responders/message-responders.js
+++ b/keyserver/src/responders/message-responders.js
@@ -55,6 +55,7 @@
   threadID: t.String,
   localID: t.maybe(t.String),
   text: t.String,
+  sidebarCreation: t.maybe(t.Boolean),
 });
 async function textMessageCreationResponder(
   viewer: Viewer,
@@ -63,7 +64,7 @@
   const request: SendTextMessageRequest = input;
   await validateInput(viewer, sendTextMessageRequestInputValidator, request);
 
-  const { threadID, localID, text: rawText } = request;
+  const { threadID, localID, text: rawText, sidebarCreation } = request;
   const text = trimMessage(rawText);
   if (!text) {
     throw new ServerError('invalid_parameters');
@@ -88,6 +89,9 @@
   if (localID) {
     messageData = { ...messageData, localID };
   }
+  if (sidebarCreation) {
+    messageData = { ...messageData, sidebarCreation };
+  }
   const rawMessageInfos = await createMessages(viewer, [messageData]);
 
   return { newMessageInfo: rawMessageInfos[0] };
@@ -115,11 +119,13 @@
   tShape({
     threadID: t.String,
     localID: t.String,
+    sidebarCreation: t.maybe(t.Boolean),
     mediaIDs: t.list(t.String),
   }),
   tShape({
     threadID: t.String,
     localID: t.String,
+    sidebarCreation: t.maybe(t.Boolean),
     mediaMessageContents: t.list(tMediaMessageMedia),
   }),
 ]);
@@ -141,7 +147,7 @@
     throw new ServerError('invalid_parameters');
   }
 
-  const { threadID, localID } = request;
+  const { threadID, localID, sidebarCreation } = request;
   const hasPermission = await checkThreadPermission(
     viewer,
     threadID,
@@ -173,6 +179,7 @@
     threadID,
     creatorID: viewer.id,
     media,
+    sidebarCreation,
   });
   const [newMessageInfo] = await createMessages(viewer, [messageData]);
   const { id } = newMessageInfo;
diff --git a/lib/shared/message-utils.js b/lib/shared/message-utils.js
--- a/lib/shared/message-utils.js
+++ b/lib/shared/message-utils.js
@@ -230,14 +230,15 @@
   });
 }
 
-type MediaMessageDataCreationInput = $ReadOnly<{
-  threadID: string,
-  creatorID: string,
-  media: $ReadOnlyArray<Media>,
-  localID?: ?string,
-  time?: ?number,
+type MediaMessageDataCreationInput = {
+  +threadID: string,
+  +creatorID: string,
+  +media: $ReadOnlyArray<Media>,
+  +localID?: ?string,
+  +time?: ?number,
+  +sidebarCreation?: ?boolean,
   ...
-}>;
+};
 function createMediaMessageData(
   input: MediaMessageDataCreationInput,
 ): MultimediaMessageData {
@@ -252,7 +253,7 @@
     }
   }
 
-  const { localID, threadID, creatorID } = input;
+  const { localID, threadID, creatorID, sidebarCreation } = input;
   const time = input.time ? input.time : Date.now();
   let messageData;
   if (allMediaArePhotos) {
@@ -266,6 +267,9 @@
     if (localID) {
       messageData = { ...messageData, localID };
     }
+    if (sidebarCreation) {
+      messageData = { ...messageData, sidebarCreation };
+    }
   } else {
     messageData = ({
       type: messageTypes.MULTIMEDIA,
@@ -277,14 +281,17 @@
     if (localID) {
       messageData = { ...messageData, localID };
     }
+    if (sidebarCreation) {
+      messageData = { ...messageData, sidebarCreation };
+    }
   }
   return messageData;
 }
 
-type MediaMessageInfoCreationInput = $ReadOnly<{
+type MediaMessageInfoCreationInput = {
   ...$Exact<MediaMessageDataCreationInput>,
-  id?: ?string,
-}>;
+  +id?: ?string,
+};
 function createMediaMessageInfo(
   input: MediaMessageInfoCreationInput,
 ): RawMultimediaMessageInfo {
diff --git a/lib/types/message-types.js b/lib/types/message-types.js
--- a/lib/types/message-types.js
+++ b/lib/types/message-types.js
@@ -529,16 +529,19 @@
   +threadID: string,
   +localID?: string,
   +text: string,
+  +sidebarCreation?: boolean,
 };
 export type SendMultimediaMessageRequest =
   | {
       +threadID: string,
       +localID: string,
+      +sidebarCreation?: boolean,
       +mediaIDs: $ReadOnlyArray<string>,
     }
   | {
       +threadID: string,
       +localID: string,
+      +sidebarCreation?: boolean,
       +mediaMessageContents: $ReadOnlyArray<MediaMessageServerDBContent>,
     };