diff --git a/lib/actions/activity-actions.js b/lib/actions/activity-actions.js
--- a/lib/actions/activity-actions.js
+++ b/lib/actions/activity-actions.js
@@ -1,17 +1,27 @@
 // @flow
 
+import invariant from 'invariant';
+import * as React from 'react';
+
 import {
   extractKeyserverIDFromID,
   extractKeyserverIDFromIDOptional,
 } from '../keyserver-conn/keyserver-call-utils.js';
 import { useKeyserverCall } from '../keyserver-conn/keyserver-call.js';
 import type { CallKeyserverEndpoint } from '../keyserver-conn/keyserver-conn-types.js';
+import type { OutboundDMOperationSpecification } from '../shared/dm-ops/dm-op-utils.js';
+import { dmOperationSpecificationTypes } from '../shared/dm-ops/dm-op-utils.js';
+import { useProcessAndSendDMOperation } from '../shared/dm-ops/process-dm-ops.js';
 import type {
   ActivityUpdate,
   ActivityUpdateSuccessPayload,
   SetThreadUnreadStatusPayload,
   SetThreadUnreadStatusRequest,
 } from '../types/activity-types.js';
+import type { DMChangeThreadReadStatusOperation } from '../types/dm-ops.js';
+import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types';
+import { threadTypeIsThick } from '../types/thread-types-enum.js';
+import { useSelector } from '../utils/redux-utils.js';
 
 export type UpdateActivityInput = {
   +activityUpdates: $ReadOnlyArray<ActivityUpdate>,
@@ -98,10 +108,49 @@
     };
   };
 
-function useSetThreadUnreadStatus(): (
+function useSetThreadUnreadStatus(
+  threadInfo: ThreadInfo,
+): (
   request: SetThreadUnreadStatusRequest,
 ) => Promise<SetThreadUnreadStatusPayload> {
-  return useKeyserverCall(setThreadUnreadStatus);
+  const viewerID = useSelector(
+    state => state.currentUserInfo && state.currentUserInfo.id,
+  );
+  const processAndSendDMOperation = useProcessAndSendDMOperation();
+  const keyserverCall = useKeyserverCall(setThreadUnreadStatus);
+
+  return React.useCallback(
+    async (input: SetThreadUnreadStatusRequest) => {
+      if (!threadTypeIsThick(threadInfo.type)) {
+        return await keyserverCall(input);
+      }
+
+      invariant(viewerID, 'viewerID must be set');
+      const op: DMChangeThreadReadStatusOperation = {
+        type: 'change_thread_read_status',
+        time: Date.now(),
+        threadID: threadInfo.id,
+        creatorID: viewerID,
+        unread: !threadInfo.currentUser.unread,
+      };
+
+      const opSpecification: OutboundDMOperationSpecification = {
+        type: dmOperationSpecificationTypes.OUTBOUND,
+        op,
+        recipients: {
+          type: 'self_devices',
+        },
+      };
+
+      await processAndSendDMOperation(opSpecification);
+      return {
+        resetToUnread: false,
+        threadID: threadInfo.id,
+      };
+    },
+
+    [keyserverCall, threadInfo, viewerID, processAndSendDMOperation],
+  );
 }
 
 export {
diff --git a/lib/hooks/toggle-unread-status.js b/lib/hooks/toggle-unread-status.js
--- a/lib/hooks/toggle-unread-status.js
+++ b/lib/hooks/toggle-unread-status.js
@@ -22,7 +22,9 @@
   const { currentUser } = threadInfo;
   const boundSetThreadUnreadStatus: (
     request: SetThreadUnreadStatusRequest,
-  ) => Promise<SetThreadUnreadStatusPayload> = useSetThreadUnreadStatus();
+  ) => Promise<SetThreadUnreadStatusPayload> =
+    useSetThreadUnreadStatus(threadInfo);
+
   const toggleUnreadStatus = React.useCallback(() => {
     const request = {
       threadID: threadInfo.id,
@@ -40,7 +42,7 @@
     );
     afterAction();
   }, [
-    threadInfo.id,
+    threadInfo,
     currentUser.unread,
     mostRecentNonLocalMessage,
     dispatchActionPromise,