diff --git a/lib/actions/aux-user-actions.js b/lib/actions/aux-user-actions.js
new file mode 100644
--- /dev/null
+++ b/lib/actions/aux-user-actions.js
@@ -0,0 +1,5 @@
+// @flow
+
+const setFarcasterFriendsFIDActionType = 'SET_FARCASTER_FRIENDS_FID';
+
+export { setFarcasterFriendsFIDActionType };
diff --git a/lib/reducers/aux-user-reducer.js b/lib/reducers/aux-user-reducer.js
new file mode 100644
--- /dev/null
+++ b/lib/reducers/aux-user-reducer.js
@@ -0,0 +1,46 @@
+// @flow
+
+import { setFarcasterFriendsFIDActionType } from '../actions/aux-user-actions.js';
+import {
+  auxUserStoreOpsHandlers,
+  type AuxUserStoreOperation,
+  type ReplaceAuxUserInfoOperation,
+} from '../ops/aux-user-store-ops.js';
+import type { AuxUserStore } from '../types/aux-user-types.js';
+import type { BaseAction } from '../types/redux-types';
+
+const { processStoreOperations: processStoreOps } = auxUserStoreOpsHandlers;
+
+function reduceAuxUserStore(
+  state: AuxUserStore,
+  action: BaseAction,
+): {
+  +auxUserStore: AuxUserStore,
+  +auxUserStoreOperations: $ReadOnlyArray<AuxUserStoreOperation>,
+} {
+  if (action.type === setFarcasterFriendsFIDActionType) {
+    const replaceOperations: ReplaceAuxUserInfoOperation[] = [];
+    action.payload.farcasterUsers.map(farcasterUser => {
+      replaceOperations.push({
+        type: 'replace_aux_user_info',
+        payload: {
+          id: farcasterUser.userID,
+          auxUserInfo: {
+            ...state.auxUserInfos[farcasterUser.userID],
+            fid: farcasterUser.farcasterID,
+          },
+        },
+      });
+    });
+    return {
+      auxUserStore: processStoreOps(state, replaceOperations),
+      auxUserStoreOperations: replaceOperations,
+    };
+  }
+  return {
+    auxUserStore: state,
+    auxUserStoreOperations: [],
+  };
+}
+
+export { reduceAuxUserStore };
diff --git a/lib/reducers/aux-user-reducer.test.js b/lib/reducers/aux-user-reducer.test.js
new file mode 100644
--- /dev/null
+++ b/lib/reducers/aux-user-reducer.test.js
@@ -0,0 +1,38 @@
+// @flow
+
+import { reduceAuxUserStore } from './aux-user-reducer.js';
+import { setFarcasterFriendsFIDActionType } from '../actions/aux-user-actions.js';
+
+jest.mock('../utils/config.js');
+
+describe('reduceAuxUserStore', () => {
+  it('should update aux user store with new thread hash', () => {
+    const oldAuxUserStore = {
+      auxUserInfos: {},
+    };
+
+    const updateAuxUserInfosAction = {
+      type: setFarcasterFriendsFIDActionType,
+      payload: {
+        farcasterUsers: [
+          {
+            userID: 'userID_1',
+            username: 'username_1',
+            farcasterID: 'farcasterID_1',
+          },
+        ],
+      },
+    };
+
+    expect(
+      reduceAuxUserStore(oldAuxUserStore, updateAuxUserInfosAction)
+        .auxUserStore,
+    ).toEqual({
+      auxUserInfos: {
+        userID_1: {
+          fid: 'farcasterID_1',
+        },
+      },
+    });
+  });
+});
diff --git a/lib/types/aux-user-types.js b/lib/types/aux-user-types.js
--- a/lib/types/aux-user-types.js
+++ b/lib/types/aux-user-types.js
@@ -1,5 +1,7 @@
 // @flow
 
+import type { FarcasterUser } from './identity-service-types';
+
 export type AuxUserInfo = { +fid: string };
 
 export type AuxUserInfos = { +[userID: string]: AuxUserInfo };
@@ -7,3 +9,7 @@
 export type AuxUserStore = {
   +auxUserInfos: AuxUserInfos,
 };
+
+export type SetFarcasterFriendsFIDPayload = {
+  +farcasterUsers: $ReadOnlyArray<FarcasterUser>,
+};
diff --git a/lib/types/redux-types.js b/lib/types/redux-types.js
--- a/lib/types/redux-types.js
+++ b/lib/types/redux-types.js
@@ -15,6 +15,7 @@
   QueueActivityUpdatesPayload,
   SetThreadUnreadStatusPayload,
 } from './activity-types.js';
+import type { SetFarcasterFriendsFIDPayload } from './aux-user-types.js';
 import type {
   UpdateUserAvatarRequest,
   UpdateUserAvatarResponse,
@@ -1366,6 +1367,10 @@
         +type: 'SET_ACTIVE_SESSION_RECOVERY',
         +payload: SetActiveSessionRecoveryPayload,
       }
+    | {
+        +type: 'SET_FARCASTER_FRIENDS_FID',
+        +payload: SetFarcasterFriendsFIDPayload,
+      }
     | {
         +type: 'OPS_PROCESSING_FINISHED_ACTION_TYPE',
         +payload?: void,