diff --git a/web/chat/chat-input-bar.react.js b/web/chat/chat-input-bar.react.js
index cb9d7463d..d71cef502 100644
--- a/web/chat/chat-input-bar.react.js
+++ b/web/chat/chat-input-bar.react.js
@@ -1,483 +1,577 @@
 // @flow
 
 import invariant from 'invariant';
 import _difference from 'lodash/fp/difference';
 import * as React from 'react';
 
 import {
   joinThreadActionTypes,
   joinThread,
   newThreadActionTypes,
 } from 'lib/actions/thread-actions';
 import { createLoadingStatusSelector } from 'lib/selectors/loading-selectors';
+import {
+  userStoreSearchIndex,
+  relativeMemberInfoSelectorForMembersOfThread,
+} from 'lib/selectors/user-selectors';
 import { localIDPrefix, trimMessage } from 'lib/shared/message-utils';
+import SearchIndex from 'lib/shared/search-index';
 import {
   threadHasPermission,
   viewerIsMember,
   threadFrozenDueToViewerBlock,
   threadActualMembers,
   checkIfDefaultMembersAreVoiced,
 } from 'lib/shared/thread-utils';
 import type { CalendarQuery } from 'lib/types/entry-types';
 import type { LoadingStatus } from 'lib/types/loading-types';
 import { messageTypes } from 'lib/types/message-types';
 import {
   type ThreadInfo,
   threadPermissions,
   type ClientThreadJoinRequest,
   type ThreadJoinPayload,
 } from 'lib/types/thread-types';
+import type { RelativeMemberInfo } from 'lib/types/thread-types';
 import { type UserInfos } from 'lib/types/user-types';
 import {
   type DispatchActionPromise,
   useServerCall,
   useDispatchActionPromise,
 } from 'lib/utils/action-utils';
 
 import Button from '../components/button.react';
 import {
   type InputState,
   type PendingMultimediaUpload,
 } from '../input/input-state';
 import LoadingIndicator from '../loading-indicator.react';
 import { allowedMimeTypeString } from '../media/file-utils';
 import Multimedia from '../media/multimedia.react';
 import { useSelector } from '../redux/redux-utils';
 import { nonThreadCalendarQuery } from '../selectors/nav-selectors';
 import SWMansionIcon from '../SWMansionIcon.react';
 import css from './chat-input-bar.css';
-
+import MentionSuggestionTooltip from './mention-suggestion-tooltip.react';
+import { mentionRegex } from './mention-utils';
 type BaseProps = {
   +threadInfo: ThreadInfo,
   +inputState: InputState,
 };
 type Props = {
   ...BaseProps,
   // Redux state
   +viewerID: ?string,
   +joinThreadLoadingStatus: LoadingStatus,
   +threadCreationInProgress: boolean,
   +calendarQuery: () => CalendarQuery,
   +nextLocalID: number,
   +isThreadActive: boolean,
   +userInfos: UserInfos,
   // Redux dispatch functions
   +dispatchActionPromise: DispatchActionPromise,
   // async functions that hit server APIs
   +joinThread: (request: ClientThreadJoinRequest) => Promise<ThreadJoinPayload>,
+  +userSearchIndex: SearchIndex,
+  +threadMembers: $ReadOnlyArray<RelativeMemberInfo>,
+  +typeaheadMatchedStrings: ?TypeaheadMatchedStrings,
+};
+export type TypeaheadMatchedStrings = {
+  +entireText: string,
+  +textBeforeAtSymbol: string,
+  +usernamePrefix: string,
 };
 class ChatInputBar extends React.PureComponent<Props> {
   textarea: ?HTMLTextAreaElement;
   multimediaInput: ?HTMLInputElement;
 
   componentDidMount() {
     this.updateHeight();
     if (this.props.isThreadActive) {
       this.addReplyListener();
     }
   }
 
   componentWillUnmount() {
     if (this.props.isThreadActive) {
       this.removeReplyListener();
     }
   }
 
   componentDidUpdate(prevProps: Props) {
     if (this.props.isThreadActive && !prevProps.isThreadActive) {
       this.addReplyListener();
     } else if (!this.props.isThreadActive && prevProps.isThreadActive) {
       this.removeReplyListener();
     }
 
     const { inputState } = this.props;
     const prevInputState = prevProps.inputState;
     if (inputState.draft !== prevInputState.draft) {
       this.updateHeight();
     }
     const curUploadIDs = ChatInputBar.unassignedUploadIDs(
       inputState.pendingUploads,
     );
     const prevUploadIDs = ChatInputBar.unassignedUploadIDs(
       prevInputState.pendingUploads,
     );
     if (
       this.multimediaInput &&
       _difference(prevUploadIDs)(curUploadIDs).length > 0
     ) {
       // Whenever a pending upload is removed, we reset the file
       // HTMLInputElement's value field, so that if the same upload occurs again
       // the onChange call doesn't get filtered
       this.multimediaInput.value = '';
     } else if (
       this.textarea &&
       _difference(curUploadIDs)(prevUploadIDs).length > 0
     ) {
       // Whenever a pending upload is added, we focus the textarea
       this.textarea.focus();
       return;
     }
 
-    if (this.props.threadInfo.id !== prevProps.threadInfo.id && this.textarea) {
+    if (
+      (this.props.threadInfo.id !== prevProps.threadInfo.id ||
+        (inputState.textCursorPosition !== prevInputState.textCursorPosition &&
+          this.textarea?.selectionStart === this.textarea?.selectionEnd)) &&
+      this.textarea
+    ) {
       this.textarea.focus();
+
+      this.textarea?.setSelectionRange(
+        inputState.textCursorPosition,
+        inputState.textCursorPosition,
+        'none',
+      );
     }
   }
 
   static unassignedUploadIDs(
     pendingUploads: $ReadOnlyArray<PendingMultimediaUpload>,
   ) {
     return pendingUploads
       .filter(
         (pendingUpload: PendingMultimediaUpload) => !pendingUpload.messageID,
       )
       .map((pendingUpload: PendingMultimediaUpload) => pendingUpload.localID);
   }
 
   updateHeight() {
     const textarea = this.textarea;
     if (textarea) {
       textarea.style.height = 'auto';
       const newHeight = Math.min(textarea.scrollHeight, 150);
       textarea.style.height = `${newHeight}px`;
     }
   }
 
   addReplyListener() {
     invariant(
       this.props.inputState,
       'inputState should be set in addReplyListener',
     );
     this.props.inputState.addReplyListener(this.focusAndUpdateText);
   }
 
   removeReplyListener() {
     invariant(
       this.props.inputState,
       'inputState should be set in removeReplyListener',
     );
     this.props.inputState.removeReplyListener(this.focusAndUpdateText);
   }
 
   render() {
     const isMember = viewerIsMember(this.props.threadInfo);
     const canJoin = threadHasPermission(
       this.props.threadInfo,
       threadPermissions.JOIN_THREAD,
     );
 
     let joinButton = null;
     if (!isMember && canJoin && !this.props.threadCreationInProgress) {
       let buttonContent;
       if (this.props.joinThreadLoadingStatus === 'loading') {
         buttonContent = (
           <LoadingIndicator
             status={this.props.joinThreadLoadingStatus}
             size="medium"
             color="white"
           />
         );
       } else {
         buttonContent = (
           <>
             <SWMansionIcon icon="plus" size={24} />
             <p className={css.joinButtonText}>Join Chat</p>
           </>
         );
       }
       joinButton = (
         <div className={css.joinButtonContainer}>
           <Button
             variant="filled"
             buttonColor={{ backgroundColor: `#${this.props.threadInfo.color}` }}
             onClick={this.onClickJoin}
           >
             {buttonContent}
           </Button>
         </div>
       );
     }
 
     const { pendingUploads, cancelPendingUpload } = this.props.inputState;
     const multimediaPreviews = pendingUploads.map(pendingUpload => (
       <Multimedia
         uri={pendingUpload.uri}
         pendingUpload={pendingUpload}
         remove={cancelPendingUpload}
         multimediaCSSClass={css.multimedia}
         multimediaImageCSSClass={css.multimediaImage}
         key={pendingUpload.localID}
       />
     ));
     const previews =
       multimediaPreviews.length > 0 ? (
         <div className={css.previews}>{multimediaPreviews}</div>
       ) : null;
 
     let content;
     // If the thread is created by somebody else while the viewer is attempting
     // to create it, the threadInfo might be modified in-place and won't
     // list the viewer as a member, which will end up hiding the input. In
     // this case, we will assume that our creation action will get translated,
     // into a join and as long as members are voiced, we can show the input.
     const defaultMembersAreVoiced = checkIfDefaultMembersAreVoiced(
       this.props.threadInfo,
     );
 
     let sendButton;
     if (this.props.inputState.draft.length) {
       sendButton = (
         <a onClick={this.onSend} className={css.sendButton}>
           <SWMansionIcon
             icon="send-2"
             size={22}
             color={`#${this.props.threadInfo.color}`}
           />
         </a>
       );
     }
 
     if (
       threadHasPermission(this.props.threadInfo, threadPermissions.VOICED) ||
       (this.props.threadCreationInProgress && defaultMembersAreVoiced)
     ) {
       content = (
         <div className={css.inputBarWrapper}>
           <a className={css.multimediaUpload} onClick={this.onMultimediaClick}>
             <input
               type="file"
               onChange={this.onMultimediaFileChange}
               ref={this.multimediaInputRef}
               accept={allowedMimeTypeString}
               multiple
             />
             <SWMansionIcon
               icon="image-1"
               size={22}
               color={`#${this.props.threadInfo.color}`}
               disableFill
             />
           </a>
           <div className={css.inputBarTextInput}>
             <textarea
               rows="1"
               placeholder="Type your message"
               value={this.props.inputState.draft}
               onChange={this.onChangeMessageText}
               onKeyDown={this.onKeyDown}
+              onClick={this.onClickTextarea}
+              onSelect={this.onSelectTextarea}
               ref={this.textareaRef}
               autoFocus
             />
           </div>
           {sendButton}
         </div>
       );
     } else if (
       threadFrozenDueToViewerBlock(
         this.props.threadInfo,
         this.props.viewerID,
         this.props.userInfos,
       ) &&
       threadActualMembers(this.props.threadInfo.members).length === 2
     ) {
       content = (
         <span className={css.explanation}>
           You can&apos;t send messages to a user that you&apos;ve blocked.
         </span>
       );
     } else if (isMember) {
       content = (
         <span className={css.explanation}>
           You don&apos;t have permission to send messages.
         </span>
       );
     } else if (defaultMembersAreVoiced && canJoin) {
       content = null;
     } else {
       content = (
         <span className={css.explanation}>
           You don&apos;t have permission to send messages.
         </span>
       );
     }
 
+    let typeaheadTooltip;
+    if (this.props.typeaheadMatchedStrings && this.textarea) {
+      typeaheadTooltip = (
+        <MentionSuggestionTooltip
+          inputState={this.props.inputState}
+          textarea={this.textarea}
+          userSearchIndex={this.props.userSearchIndex}
+          threadMembers={this.props.threadMembers}
+          viewerID={this.props.viewerID}
+          matchedStrings={this.props.typeaheadMatchedStrings}
+        />
+      );
+    }
+
     return (
       <div className={css.inputBar}>
         {joinButton}
         {previews}
         {content}
+        {typeaheadTooltip}
       </div>
     );
   }
 
   textareaRef = (textarea: ?HTMLTextAreaElement) => {
     this.textarea = textarea;
     if (textarea) {
       textarea.focus();
     }
   };
 
   onChangeMessageText = (event: SyntheticEvent<HTMLTextAreaElement>) => {
     this.props.inputState.setDraft(event.currentTarget.value);
+    this.props.inputState.setTextCursorPosition(
+      event.currentTarget.selectionStart,
+    );
+  };
+
+  onClickTextarea = (event: SyntheticEvent<HTMLTextAreaElement>) => {
+    this.props.inputState.setTextCursorPosition(
+      event.currentTarget.selectionStart,
+    );
+  };
+
+  onSelectTextarea = (event: SyntheticEvent<HTMLTextAreaElement>) => {
+    this.props.inputState.setTextCursorPosition(
+      event.currentTarget.selectionStart,
+    );
   };
 
   focusAndUpdateText = (text: string) => {
     // We need to call focus() first on Safari, otherwise the cursor
     // ends up at the start instead of the end for some reason
     const { textarea } = this;
     invariant(textarea, 'textarea should be set');
     textarea.focus();
 
     // We reset the textarea to an empty string at the start so that the cursor
     // always ends up at the end, even if the text doesn't actually change
     textarea.value = '';
     const currentText = this.props.inputState.draft;
     if (!currentText.startsWith(text)) {
       const prependedText = text.concat(currentText);
       this.props.inputState.setDraft(prependedText);
       textarea.value = prependedText;
     } else {
       textarea.value = currentText;
     }
 
     // The above strategies make sure the cursor is at the end,
     // but we also need to make sure that we're scrolled to the bottom
     textarea.scrollTop = textarea.scrollHeight;
   };
 
   onKeyDown = (event: SyntheticKeyboardEvent<HTMLTextAreaElement>) => {
     if (event.keyCode === 13 && !event.shiftKey) {
       event.preventDefault();
       this.send();
     }
   };
 
   onSend = (event: SyntheticEvent<HTMLAnchorElement>) => {
     event.preventDefault();
     this.send();
   };
 
   send() {
     let { nextLocalID } = this.props;
 
     const text = trimMessage(this.props.inputState.draft);
     if (text) {
-      // TODO we should make the send button appear dynamically
-      // iff trimmed text is nonempty, just like native
       this.dispatchTextMessageAction(text, nextLocalID);
       nextLocalID++;
     }
     if (this.props.inputState.pendingUploads.length > 0) {
       this.props.inputState.createMultimediaMessage(
         nextLocalID,
         this.props.threadInfo,
       );
     }
   }
 
   dispatchTextMessageAction(text: string, nextLocalID: number) {
     this.props.inputState.setDraft('');
 
     const localID = `${localIDPrefix}${nextLocalID}`;
     const creatorID = this.props.viewerID;
     invariant(creatorID, 'should have viewer ID in order to send a message');
 
     this.props.inputState.sendTextMessage(
       {
         type: messageTypes.TEXT,
         localID,
         threadID: this.props.threadInfo.id,
         text,
         creatorID,
         time: Date.now(),
       },
       this.props.threadInfo,
     );
   }
 
   multimediaInputRef = (multimediaInput: ?HTMLInputElement) => {
     this.multimediaInput = multimediaInput;
   };
 
   onMultimediaClick = () => {
     if (this.multimediaInput) {
       this.multimediaInput.click();
     }
   };
 
   onMultimediaFileChange = async (
     event: SyntheticInputEvent<HTMLInputElement>,
   ) => {
     const result = await this.props.inputState.appendFiles([
       ...event.target.files,
     ]);
     if (!result && this.multimediaInput) {
       this.multimediaInput.value = '';
     }
   };
 
   onClickJoin = () => {
     this.props.dispatchActionPromise(joinThreadActionTypes, this.joinAction());
   };
 
   async joinAction() {
     const query = this.props.calendarQuery();
     return await this.props.joinThread({
       threadID: this.props.threadInfo.id,
       calendarQuery: {
         startDate: query.startDate,
         endDate: query.endDate,
         filters: [
           ...query.filters,
           { type: 'threads', threadIDs: [this.props.threadInfo.id] },
         ],
       },
     });
   }
 }
 
 const joinThreadLoadingStatusSelector = createLoadingStatusSelector(
   joinThreadActionTypes,
 );
 const createThreadLoadingStatusSelector = createLoadingStatusSelector(
   newThreadActionTypes,
 );
 
 const ConnectedChatInputBar: React.ComponentType<BaseProps> = React.memo<BaseProps>(
   function ConnectedChatInputBar(props) {
     const viewerID = useSelector(
       state => state.currentUserInfo && state.currentUserInfo.id,
     );
     const nextLocalID = useSelector(state => state.nextLocalID);
     const isThreadActive = useSelector(
       state => props.threadInfo.id === state.navInfo.activeChatThreadID,
     );
     const userInfos = useSelector(state => state.userStore.userInfos);
     const joinThreadLoadingStatus = useSelector(
       joinThreadLoadingStatusSelector,
     );
     const createThreadLoadingStatus = useSelector(
       createThreadLoadingStatusSelector,
     );
     const threadCreationInProgress = createThreadLoadingStatus === 'loading';
     const calendarQuery = useSelector(nonThreadCalendarQuery);
     const dispatchActionPromise = useDispatchActionPromise();
     const callJoinThread = useServerCall(joinThread);
+    const userSearchIndex = useSelector(userStoreSearchIndex);
+    const threadMembers = useSelector(
+      relativeMemberInfoSelectorForMembersOfThread(props.threadInfo.id),
+    );
+
+    const inputSliceEndingAtCursor = React.useMemo(
+      () =>
+        props.inputState.draft.slice(0, props.inputState.textCursorPosition),
+      [props.inputState.draft, props.inputState.textCursorPosition],
+    );
+    // we only try to match if there is end of text or whitespace after cursor
+    const typeaheadRegexMatches = React.useMemo(
+      () =>
+        inputSliceEndingAtCursor.length === props.inputState.draft.length ||
+        /\s/.test(props.inputState.draft[props.inputState.textCursorPosition])
+          ? inputSliceEndingAtCursor.match(mentionRegex)
+          : null,
+      [
+        inputSliceEndingAtCursor,
+        props.inputState.textCursorPosition,
+        props.inputState.draft,
+      ],
+    );
+
+    const typeaheadMatchedStrings: ?TypeaheadMatchedStrings = React.useMemo(
+      () =>
+        typeaheadRegexMatches !== null
+          ? {
+              entireText: typeaheadRegexMatches[0],
+              textBeforeAtSymbol: typeaheadRegexMatches[1],
+              usernamePrefix: typeaheadRegexMatches[2],
+            }
+          : null,
+      [typeaheadRegexMatches],
+    );
 
     return (
       <ChatInputBar
         {...props}
         viewerID={viewerID}
         joinThreadLoadingStatus={joinThreadLoadingStatus}
         threadCreationInProgress={threadCreationInProgress}
         calendarQuery={calendarQuery}
         nextLocalID={nextLocalID}
         isThreadActive={isThreadActive}
         userInfos={userInfos}
         dispatchActionPromise={dispatchActionPromise}
         joinThread={callJoinThread}
+        userSearchIndex={userSearchIndex}
+        threadMembers={threadMembers}
+        typeaheadMatchedStrings={typeaheadMatchedStrings}
       />
     );
   },
 );
 
 export default ConnectedChatInputBar;
diff --git a/web/chat/mention-suggestion-tooltip.react.js b/web/chat/mention-suggestion-tooltip.react.js
index e6fe423e5..a8a7096fa 100644
--- a/web/chat/mention-suggestion-tooltip.react.js
+++ b/web/chat/mention-suggestion-tooltip.react.js
@@ -1,110 +1,113 @@
 // @flow
 
 import * as React from 'react';
 
 import SearchIndex from 'lib/shared/search-index';
 import { threadOtherMembers } from 'lib/shared/thread-utils';
 import type { RelativeMemberInfo } from 'lib/types/thread-types';
 
 import Button from '../components/button.react';
 import type { InputState } from '../input/input-state';
+import { type TypeaheadMatchedStrings } from './chat-input-bar.react';
 import css from './mention-suggestion-tooltip.css';
 import {
   getTypeaheadTooltipActions,
   getTypeaheadTooltipPosition,
   getTypeaheadUserSuggestions,
 } from './mention-utils';
 
 export type MentionSuggestionTooltipProps = {
   +inputState: InputState,
   +textarea: HTMLTextAreaElement,
   +userSearchIndex: SearchIndex,
   +threadMembers: $ReadOnlyArray<RelativeMemberInfo>,
   +viewerID: ?string,
-  +matchedText: string,
-  +matchedTextBeforeAtSymbol: string,
-  +matchedUsernamePrefix: string,
+  +matchedStrings: TypeaheadMatchedStrings,
 };
 
 function MentionSuggestionTooltip(
   props: MentionSuggestionTooltipProps,
 ): React.Node {
   const {
     inputState,
     textarea,
     userSearchIndex,
     threadMembers,
     viewerID,
-    matchedText,
-    matchedTextBeforeAtSymbol,
-    matchedUsernamePrefix,
+    matchedStrings,
   } = props;
 
+  const {
+    entireText: matchedText,
+    textBeforeAtSymbol: matchedTextBeforeAtSymbol,
+    usernamePrefix: matchedUsernamePrefix,
+  } = matchedStrings;
+
   const typedPrefix = matchedUsernamePrefix ?? '';
 
   const suggestedUsers = React.useMemo(
     () =>
       getTypeaheadUserSuggestions(
         userSearchIndex,
         threadOtherMembers(threadMembers, viewerID),
         typedPrefix,
       ),
     [userSearchIndex, threadMembers, viewerID, typedPrefix],
   );
 
   const actions = React.useMemo(
     () =>
       getTypeaheadTooltipActions(
         inputState,
         textarea,
         suggestedUsers,
         matchedTextBeforeAtSymbol,
         matchedText,
       ),
     [
       inputState,
       textarea,
       suggestedUsers,
       matchedTextBeforeAtSymbol,
       matchedText,
     ],
   );
 
   const tooltipPosition = React.useMemo(
     () =>
       getTypeaheadTooltipPosition(
         textarea,
         actions.length,
         matchedTextBeforeAtSymbol,
       ),
     [textarea, actions.length, matchedTextBeforeAtSymbol],
   );
 
   const tooltipPositionStyle = React.useMemo(
     () => ({
       top: tooltipPosition.top,
       left: tooltipPosition.left,
     }),
     [tooltipPosition],
   );
 
   const tooltipButtons = React.useMemo(() => {
     return actions.map(({ key, onClick, actionButtonContent }) => (
       <Button key={key} onClick={onClick} className={css.suggestion}>
         <span>@{actionButtonContent}</span>
       </Button>
     ));
   }, [actions]);
 
   if (!actions || actions.length === 0) {
     return null;
   }
 
   return (
     <div className={css.suggestionsContainer} style={tooltipPositionStyle}>
       {tooltipButtons}
     </div>
   );
 }
 
 export default MentionSuggestionTooltip;