diff --git a/lib/actions/thread-actions.js b/lib/actions/thread-actions.js
--- a/lib/actions/thread-actions.js
+++ b/lib/actions/thread-actions.js
@@ -11,14 +11,19 @@
 import {
   type OutboundDMOperationSpecification,
   dmOperationSpecificationTypes,
+  getCreateThickRawThreadInfoInputFromThreadInfo,
 } from '../shared/dm-ops/dm-op-utils.js';
 import { useProcessAndSendDMOperation } from '../shared/dm-ops/process-dm-ops.js';
 import { permissionsAndAuthRelatedRequestTimeout } from '../shared/timeouts.js';
 import type {
   DMChangeThreadSettingsOperation,
   DMThreadSettingsChanges,
+  DMJoinThreadOperation,
 } from '../types/dm-ops.js';
-import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
+import type {
+  ThreadInfo,
+  RawThreadInfo,
+} from '../types/minimally-encoded-thread-permissions-types.js';
 import {
   thickThreadTypes,
   threadTypeIsThick,
@@ -346,10 +351,56 @@
     };
   };
 
-function useJoinThread(): (
-  input: ClientThreadJoinRequest,
-) => Promise<ThreadJoinPayload> {
-  return useKeyserverCall(joinThread);
+function useJoinThread(
+  rawThreadInfo: ?RawThreadInfo,
+): (input: ClientThreadJoinRequest) => Promise<ThreadJoinPayload> {
+  const processAndSendDMOperation = useProcessAndSendDMOperation();
+  const viewerID = useSelector(
+    state => state.currentUserInfo && state.currentUserInfo.id,
+  );
+  const keyserverCall = useKeyserverCall(joinThread);
+  return React.useCallback(
+    async (input: ClientThreadJoinRequest) => {
+      if (!rawThreadInfo || !rawThreadInfo.thick) {
+        return await keyserverCall(input);
+      }
+
+      invariant(viewerID, 'viewerID should be set');
+
+      const existingThreadDetails =
+        getCreateThickRawThreadInfoInputFromThreadInfo(rawThreadInfo);
+
+      const op: DMJoinThreadOperation = {
+        type: 'join_thread',
+        joinerID: viewerID,
+        time: Date.now(),
+        messageID: uuid.v4(),
+        existingThreadDetails,
+      };
+
+      const opSpecification: OutboundDMOperationSpecification = {
+        type: dmOperationSpecificationTypes.OUTBOUND,
+        op,
+        recipients: {
+          type: 'all_thread_members',
+          threadID:
+            rawThreadInfo.type === thickThreadTypes.THICK_SIDEBAR &&
+            rawThreadInfo.parentThreadID
+              ? rawThreadInfo.parentThreadID
+              : rawThreadInfo.id,
+        },
+      };
+
+      await processAndSendDMOperation(opSpecification);
+      return ({
+        updatesResult: { newUpdates: [] },
+        rawMessageInfos: [],
+        truncationStatuses: {},
+        userInfos: [],
+      }: ThreadJoinPayload);
+    },
+    [keyserverCall, processAndSendDMOperation, viewerID, rawThreadInfo],
+  );
 }
 
 export type LeaveThreadInput = {
diff --git a/lib/shared/community-utils.js b/lib/shared/community-utils.js
--- a/lib/shared/community-utils.js
+++ b/lib/shared/community-utils.js
@@ -210,7 +210,12 @@
 
   const dispatch = useDispatch();
   const dispatchActionPromise = useDispatchActionPromise();
-  const callJoinThread = useJoinThread();
+  const rawThreadInfo = useSelector(state =>
+    threadID ? state.threadStore.threadInfos[threadID] : null,
+  );
+
+  const callJoinThread = useJoinThread(rawThreadInfo);
+  const callJoinCommunityThread = useJoinThread();
 
   let keyserverID = keyserverOverride?.keyserverID;
   if (!keyserverID && communityID) {
@@ -338,7 +343,7 @@
       }
       const communityThreadID = ongoingJoinData.communityID;
       const query = calendarQuery();
-      const joinThreadPromise = callJoinThread({
+      const joinThreadPromise = callJoinCommunityThread({
         threadID: communityThreadID,
         calendarQuery: {
           startDate: query.startDate,
@@ -372,6 +377,7 @@
       }
     })();
   }, [
+    callJoinCommunityThread,
     calendarQuery,
     callJoinThread,
     defaultSubscription,
diff --git a/lib/shared/dm-ops/dm-op-utils.js b/lib/shared/dm-ops/dm-op-utils.js
--- a/lib/shared/dm-ops/dm-op-utils.js
+++ b/lib/shared/dm-ops/dm-op-utils.js
@@ -238,4 +238,8 @@
   );
 }
 
-export { createMessagesToPeersFromDMOp, useAddDMThreadMembers };
+export {
+  createMessagesToPeersFromDMOp,
+  useAddDMThreadMembers,
+  getCreateThickRawThreadInfoInputFromThreadInfo,
+};
diff --git a/lib/types/thread-types.js b/lib/types/thread-types.js
--- a/lib/types/thread-types.js
+++ b/lib/types/thread-types.js
@@ -365,7 +365,7 @@
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +truncationStatuses: MessageTruncationStatuses,
   +userInfos: $ReadOnlyArray<UserInfo>,
-  +keyserverID: string,
+  +keyserverID?: string,
 };
 
 export type ThreadFetchMediaResult = {
diff --git a/native/chat/chat-input-bar.react.js b/native/chat/chat-input-bar.react.js
--- a/native/chat/chat-input-bar.react.js
+++ b/native/chat/chat-input-bar.react.js
@@ -1243,7 +1243,10 @@
 
   const dispatch = useDispatch();
   const dispatchActionPromise = useDispatchActionPromise();
-  const callJoinThread = useJoinThread();
+  const rawThreadInfo = useSelector(
+    state => state.threadStore.threadInfos[props.threadInfo.id],
+  );
+  const callJoinThread = useJoinThread(rawThreadInfo);
 
   const { getChatMentionSearchIndex } = useChatMentionContext();
   const chatMentionSearchIndex = getChatMentionSearchIndex(props.threadInfo);
diff --git a/web/chat/chat-input-bar.react.js b/web/chat/chat-input-bar.react.js
--- a/web/chat/chat-input-bar.react.js
+++ b/web/chat/chat-input-bar.react.js
@@ -573,7 +573,10 @@
     const threadCreationInProgress = createThreadLoadingStatus === 'loading';
     const calendarQuery = useSelector(nonThreadCalendarQuery);
     const dispatchActionPromise = useDispatchActionPromise();
-    const callJoinThread = useJoinThread();
+    const rawThreadInfo = useSelector(
+      state => state.threadStore.threadInfos[props.threadInfo.id],
+    );
+    const callJoinThread = useJoinThread(rawThreadInfo);
     const { getChatMentionSearchIndex } = useChatMentionContext();
     const chatMentionSearchIndex = getChatMentionSearchIndex(props.threadInfo);