diff --git a/app/javascript/mastodon/actions/markers.js b/app/javascript/mastodon/actions/markers.js
deleted file mode 100644
index cfc329a8b7..0000000000
--- a/app/javascript/mastodon/actions/markers.js
+++ /dev/null
@@ -1,152 +0,0 @@
-import { List as ImmutableList } from 'immutable';
-
-import { debounce } from 'lodash';
-
-import api from '../api';
-import { compareId } from '../compare_id';
-
-export const MARKERS_FETCH_REQUEST = 'MARKERS_FETCH_REQUEST';
-export const MARKERS_FETCH_SUCCESS = 'MARKERS_FETCH_SUCCESS';
-export const MARKERS_FETCH_FAIL    = 'MARKERS_FETCH_FAIL';
-export const MARKERS_SUBMIT_SUCCESS = 'MARKERS_SUBMIT_SUCCESS';
-
-export const synchronouslySubmitMarkers = () => (dispatch, getState) => {
-  const accessToken = getState().getIn(['meta', 'access_token'], '');
-  const params      = _buildParams(getState());
-
-  if (Object.keys(params).length === 0 || accessToken === '') {
-    return;
-  }
-
-  // The Fetch API allows us to perform requests that will be carried out
-  // after the page closes. But that only works if the `keepalive` attribute
-  // is supported.
-  if (window.fetch && 'keepalive' in new Request('')) {
-    fetch('/api/v1/markers', {
-      keepalive: true,
-      method: 'POST',
-      headers: {
-        'Content-Type': 'application/json',
-        'Authorization': `Bearer ${accessToken}`,
-      },
-      body: JSON.stringify(params),
-    });
-
-    return;
-  } else if (navigator && navigator.sendBeacon) {
-    // Failing that, we can use sendBeacon, but we have to encode the data as
-    // FormData for DoorKeeper to recognize the token.
-    const formData = new FormData();
-
-    formData.append('bearer_token', accessToken);
-
-    for (const [id, value] of Object.entries(params)) {
-      formData.append(`${id}[last_read_id]`, value.last_read_id);
-    }
-
-    if (navigator.sendBeacon('/api/v1/markers', formData)) {
-      return;
-    }
-  }
-
-  // If neither Fetch nor sendBeacon worked, try to perform a synchronous
-  // request.
-  try {
-    const client = new XMLHttpRequest();
-
-    client.open('POST', '/api/v1/markers', false);
-    client.setRequestHeader('Content-Type', 'application/json');
-    client.setRequestHeader('Authorization', `Bearer ${accessToken}`);
-    client.send(JSON.stringify(params));
-  } catch (e) {
-    // Do not make the BeforeUnload handler error out
-  }
-};
-
-const _buildParams = (state) => {
-  const params = {};
-
-  const lastHomeId         = state.getIn(['timelines', 'home', 'items'], ImmutableList()).find(item => item !== null);
-  const lastNotificationId = state.getIn(['notifications', 'lastReadId']);
-
-  if (lastHomeId && compareId(lastHomeId, state.getIn(['markers', 'home'])) > 0) {
-    params.home = {
-      last_read_id: lastHomeId,
-    };
-  }
-
-  if (lastNotificationId && compareId(lastNotificationId, state.getIn(['markers', 'notifications'])) > 0) {
-    params.notifications = {
-      last_read_id: lastNotificationId,
-    };
-  }
-
-  return params;
-};
-
-const debouncedSubmitMarkers = debounce((dispatch, getState) => {
-  const accessToken = getState().getIn(['meta', 'access_token'], '');
-  const params      = _buildParams(getState());
-
-  if (Object.keys(params).length === 0 || accessToken === '') {
-    return;
-  }
-
-  api(getState).post('/api/v1/markers', params).then(() => {
-    dispatch(submitMarkersSuccess(params));
-  }).catch(() => {});
-}, 300000, { leading: true, trailing: true });
-
-export function submitMarkersSuccess({ home, notifications }) {
-  return {
-    type: MARKERS_SUBMIT_SUCCESS,
-    home: (home || {}).last_read_id,
-    notifications: (notifications || {}).last_read_id,
-  };
-}
-
-export function submitMarkers(params = {}) {
-  const result = (dispatch, getState) => debouncedSubmitMarkers(dispatch, getState);
-
-  if (params.immediate === true) {
-    debouncedSubmitMarkers.flush();
-  }
-
-  return result;
-}
-
-export const fetchMarkers = () => (dispatch, getState) => {
-  const params = { timeline: ['notifications'] };
-
-  dispatch(fetchMarkersRequest());
-
-  api(getState).get('/api/v1/markers', { params }).then(response => {
-    dispatch(fetchMarkersSuccess(response.data));
-  }).catch(error => {
-    dispatch(fetchMarkersFail(error));
-  });
-};
-
-export function fetchMarkersRequest() {
-  return {
-    type: MARKERS_FETCH_REQUEST,
-    skipLoading: true,
-  };
-}
-
-export function fetchMarkersSuccess(markers) {
-  return {
-    type: MARKERS_FETCH_SUCCESS,
-    markers,
-    skipLoading: true,
-  };
-}
-
-export function fetchMarkersFail(error) {
-  return {
-    type: MARKERS_FETCH_FAIL,
-    error,
-    skipLoading: true,
-    skipAlert: true,
-  };
-}
diff --git a/app/javascript/mastodon/actions/markers.ts b/app/javascript/mastodon/actions/markers.ts
new file mode 100644
index 0000000000..4e90a9c6bd
--- /dev/null
+++ b/app/javascript/mastodon/actions/markers.ts
@@ -0,0 +1,163 @@
+import { List as ImmutableList } from 'immutable';
+
+import { debounce } from 'lodash';
+
+import type { MarkerJSON } from 'mastodon/api_types/markers';
+import type { RootState } from 'mastodon/store';
+import { createAppAsyncThunk } from 'mastodon/store/typed_functions';
+
+import api, { authorizationTokenFromState } from '../api';
+import { compareId } from '../compare_id';
+
+export const synchronouslySubmitMarkers = createAppAsyncThunk(
+  'markers/submit',
+  async (_args, { getState }) => {
+    const accessToken = authorizationTokenFromState(getState);
+    const params = buildPostMarkersParams(getState());
+
+    if (Object.keys(params).length === 0 || !accessToken) {
+      return;
+    }
+
+    // The Fetch API allows us to perform requests that will be carried out
+    // after the page closes. But that only works if the `keepalive` attribute
+    // is supported.
+    if ('fetch' in window && 'keepalive' in new Request('')) {
+      await fetch('/api/v1/markers', {
+        keepalive: true,
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          Authorization: `Bearer ${accessToken}`,
+        },
+        body: JSON.stringify(params),
+      });
+
+      return;
+      // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+    } else if ('navigator' && 'sendBeacon' in navigator) {
+      // Failing that, we can use sendBeacon, but we have to encode the data as
+      // FormData for DoorKeeper to recognize the token.
+      const formData = new FormData();
+
+      formData.append('bearer_token', accessToken);
+
+      for (const [id, value] of Object.entries(params)) {
+        if (value.last_read_id)
+          formData.append(`${id}[last_read_id]`, value.last_read_id);
+      }
+
+      if (navigator.sendBeacon('/api/v1/markers', formData)) {
+        return;
+      }
+    }
+
+    // If neither Fetch nor sendBeacon worked, try to perform a synchronous
+    // request.
+    try {
+      const client = new XMLHttpRequest();
+
+      client.open('POST', '/api/v1/markers', false);
+      client.setRequestHeader('Content-Type', 'application/json');
+      client.setRequestHeader('Authorization', `Bearer ${accessToken}`);
+      client.send(JSON.stringify(params));
+    } catch (e) {
+      // Do not make the BeforeUnload handler error out
+    }
+  },
+);
+
+interface MarkerParam {
+  last_read_id?: string;
+}
+
+function getLastHomeId(state: RootState): string | undefined {
+  /* eslint-disable @typescript-eslint/no-unsafe-return, @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-member-access */
+  return (
+    state
+      // @ts-expect-error state.timelines is not yet typed
+      .getIn(['timelines', 'home', 'items'], ImmutableList())
+      // @ts-expect-error state.timelines is not yet typed
+      .find((item) => item !== null)
+  );
+}
+
+function getLastNotificationId(state: RootState): string | undefined {
+  // @ts-expect-error state.notifications is not yet typed
+  return state.getIn(['notifications', 'lastReadId']);
+}
+
+const buildPostMarkersParams = (state: RootState) => {
+  const params = {} as { home?: MarkerParam; notifications?: MarkerParam };
+
+  const lastHomeId = getLastHomeId(state);
+  const lastNotificationId = getLastNotificationId(state);
+
+  if (lastHomeId && compareId(lastHomeId, state.markers.home) > 0) {
+    params.home = {
+      last_read_id: lastHomeId,
+    };
+  }
+
+  if (
+    lastNotificationId &&
+    compareId(lastNotificationId, state.markers.notifications) > 0
+  ) {
+    params.notifications = {
+      last_read_id: lastNotificationId,
+    };
+  }
+
+  return params;
+};
+
+export const submitMarkersAction = createAppAsyncThunk<{
+  home: string | undefined;
+  notifications: string | undefined;
+}>('markers/submitAction', async (_args, { getState }) => {
+  const accessToken = authorizationTokenFromState(getState);
+  const params = buildPostMarkersParams(getState());
+
+  if (Object.keys(params).length === 0 || accessToken === '') {
+    return { home: undefined, notifications: undefined };
+  }
+
+  await api(getState).post<MarkerJSON>('/api/v1/markers', params);
+
+  return {
+    home: params.home?.last_read_id,
+    notifications: params.notifications?.last_read_id,
+  };
+});
+
+const debouncedSubmitMarkers = debounce(
+  (dispatch) => {
+    dispatch(submitMarkersAction());
+  },
+  300000,
+  {
+    leading: true,
+    trailing: true,
+  },
+);
+
+export const submitMarkers = createAppAsyncThunk(
+  'markers/submit',
+  (params: { immediate?: boolean }, { dispatch }) => {
+    debouncedSubmitMarkers(dispatch);
+
+    if (params.immediate) {
+      debouncedSubmitMarkers.flush();
+    }
+  },
+);
+
+export const fetchMarkers = createAppAsyncThunk(
+  'markers/fetch',
+  async (_args, { getState }) => {
+    const response =
+      await api(getState).get<Record<string, MarkerJSON>>(`/api/v1/markers`);
+
+    return { markers: response.data };
+  },
+);
diff --git a/app/javascript/mastodon/api.ts b/app/javascript/mastodon/api.ts
index f262fd8570..de597a3e3b 100644
--- a/app/javascript/mastodon/api.ts
+++ b/app/javascript/mastodon/api.ts
@@ -29,9 +29,14 @@ const setCSRFHeader = () => {
 
 void ready(setCSRFHeader);
 
+export const authorizationTokenFromState = (getState?: GetState) => {
+  return (
+    getState && (getState().meta.get('access_token', '') as string | false)
+  );
+};
+
 const authorizationHeaderFromState = (getState?: GetState) => {
-  const accessToken =
-    getState && (getState().meta.get('access_token', '') as string);
+  const accessToken = authorizationTokenFromState(getState);
 
   if (!accessToken) {
     return {};
diff --git a/app/javascript/mastodon/api_types/markers.ts b/app/javascript/mastodon/api_types/markers.ts
new file mode 100644
index 0000000000..f7664fd7c1
--- /dev/null
+++ b/app/javascript/mastodon/api_types/markers.ts
@@ -0,0 +1,7 @@
+// See app/serializers/rest/account_serializer.rb
+
+export interface MarkerJSON {
+  last_read_id: string;
+  version: string;
+  updated_at: string;
+}
diff --git a/app/javascript/mastodon/reducers/index.ts b/app/javascript/mastodon/reducers/index.ts
index 3d42cc83f8..b88175e777 100644
--- a/app/javascript/mastodon/reducers/index.ts
+++ b/app/javascript/mastodon/reducers/index.ts
@@ -21,7 +21,7 @@ import history from './history';
 import listAdder from './list_adder';
 import listEditor from './list_editor';
 import lists from './lists';
-import markers from './markers';
+import { markersReducer } from './markers';
 import media_attachments from './media_attachments';
 import meta from './meta';
 import { modalReducer } from './modal';
@@ -77,7 +77,7 @@ const reducers = {
   suggestions,
   polls,
   trends,
-  markers,
+  markers: markersReducer,
   picture_in_picture,
   history,
   tags,
diff --git a/app/javascript/mastodon/reducers/markers.js b/app/javascript/mastodon/reducers/markers.js
deleted file mode 100644
index c7c5d99f61..0000000000
--- a/app/javascript/mastodon/reducers/markers.js
+++ /dev/null
@@ -1,26 +0,0 @@
-import { Map as ImmutableMap } from 'immutable';
-
-import {
-  MARKERS_SUBMIT_SUCCESS,
-} from '../actions/markers';
-
-
-const initialState = ImmutableMap({
-  home: '0',
-  notifications: '0',
-});
-
-export default function markers(state = initialState, action) {
-  switch(action.type) {
-  case MARKERS_SUBMIT_SUCCESS:
-    if (action.home) {
-      state = state.set('home', action.home);
-    }
-    if (action.notifications) {
-      state = state.set('notifications', action.notifications);
-    }
-    return state;
-  default:
-    return state;
-  }
-}
diff --git a/app/javascript/mastodon/reducers/markers.ts b/app/javascript/mastodon/reducers/markers.ts
new file mode 100644
index 0000000000..ec85d0f173
--- /dev/null
+++ b/app/javascript/mastodon/reducers/markers.ts
@@ -0,0 +1,18 @@
+import { createReducer } from '@reduxjs/toolkit';
+
+import { submitMarkersAction } from 'mastodon/actions/markers';
+
+const initialState = {
+  home: '0',
+  notifications: '0',
+};
+
+export const markersReducer = createReducer(initialState, (builder) => {
+  builder.addCase(
+    submitMarkersAction.fulfilled,
+    (state, { payload: { home, notifications } }) => {
+      if (home) state.home = home;
+      if (notifications) state.notifications = notifications;
+    },
+  );
+});
diff --git a/app/javascript/mastodon/reducers/notifications.js b/app/javascript/mastodon/reducers/notifications.js
index bc85936439..7230fabcae 100644
--- a/app/javascript/mastodon/reducers/notifications.js
+++ b/app/javascript/mastodon/reducers/notifications.js
@@ -13,7 +13,7 @@ import {
   unfocusApp,
 } from '../actions/app';
 import {
-  MARKERS_FETCH_SUCCESS,
+  fetchMarkers,
 } from '../actions/markers';
 import {
   notificationsUpdate,
@@ -255,8 +255,8 @@ const recountUnread = (state, last_read_id) => {
 
 export default function notifications(state = initialState, action) {
   switch(action.type) {
-  case MARKERS_FETCH_SUCCESS:
-    return action.markers.notifications ? recountUnread(state, action.markers.notifications.last_read_id) : state;
+  case fetchMarkers.fulfilled.type:
+    return action.payload.markers.notifications ? recountUnread(state, action.payload.markers.notifications.last_read_id) : state;
   case NOTIFICATIONS_MOUNT:
     return updateMounted(state);
   case NOTIFICATIONS_UNMOUNT:
diff --git a/app/serializers/rest/marker_serializer.rb b/app/serializers/rest/marker_serializer.rb
index 2eaf3d5076..b0c1c553ff 100644
--- a/app/serializers/rest/marker_serializer.rb
+++ b/app/serializers/rest/marker_serializer.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class REST::MarkerSerializer < ActiveModel::Serializer
+  # Please update `app/javascript/mastodon/api_types/markers.ts` when making changes to the attributes
+
   attributes :last_read_id, :version, :updated_at
 
   def last_read_id