diff --git a/lib/selectors/nav-selectors.js b/lib/selectors/nav-selectors.js
--- a/lib/selectors/nav-selectors.js
+++ b/lib/selectors/nav-selectors.js
@@ -19,7 +19,6 @@
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import type { BaseNavInfo } from '../types/nav-types.js';
 import type { BaseAppState } from '../types/redux-types.js';
-import type { LegacyRelativeMemberInfo } from '../types/thread-types';
 import type { UserInfo } from '../types/user-types.js';
 import { getConfig } from '../utils/config.js';
 import { values } from '../utils/objects.js';
@@ -84,16 +83,14 @@
 const useENSNamesOptions = { allAtOnce: true };
 
 function useUserSearchIndex(
-  userInfos: $ReadOnlyArray<
-    UserInfo | LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
-  >,
+  userInfos: $ReadOnlyArray<UserInfo | MinimallyEncodedRelativeMemberInfo>,
 ): SearchIndex {
   const membersWithENSNames = useENSNames(userInfos, useENSNamesOptions);
 
   const memberMap = React.useMemo(() => {
     const result = new Map<
       string,
-      UserInfo | LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
+      UserInfo | MinimallyEncodedRelativeMemberInfo,
     >();
     for (const userInfo of membersWithENSNames) {
       result.set(userInfo.id, userInfo);
diff --git a/lib/shared/mention-utils.js b/lib/shared/mention-utils.js
--- a/lib/shared/mention-utils.js
+++ b/lib/shared/mention-utils.js
@@ -13,10 +13,7 @@
   ThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadTypes } from '../types/thread-types-enum.js';
-import type {
-  ChatMentionCandidates,
-  LegacyRelativeMemberInfo,
-} from '../types/thread-types.js';
+import type { ChatMentionCandidates } from '../types/thread-types.js';
 import { chatNameMaxLength, idSchemaRegex } from '../utils/validation-utils.js';
 
 export type TypeaheadMatchedStrings = {
@@ -31,7 +28,7 @@
 
 type MentionTypeaheadUserSuggestionItem = {
   +type: 'user',
-  +userInfo: LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
+  +userInfo: MinimallyEncodedRelativeMemberInfo,
 };
 
 type MentionTypeaheadChatSuggestionItem = {
@@ -108,9 +105,7 @@
 
 const useENSNamesOptions = { allAtOnce: true };
 function useMentionTypeaheadUserSuggestions(
-  threadMembers: $ReadOnlyArray<
-    LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
-  >,
+  threadMembers: $ReadOnlyArray<MinimallyEncodedRelativeMemberInfo>,
   typeaheadMatchedStrings: ?TypeaheadMatchedStrings,
 ): $ReadOnlyArray<MentionTypeaheadUserSuggestionItem> {
   const userSearchIndex = useUserSearchIndex(threadMembers);
diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -92,7 +92,6 @@
   ChangeThreadSettingsPayload,
   ClientNewThreadRequest,
   LegacyRawThreadInfo,
-  LegacyRelativeMemberInfo,
   MemberInfo,
   MixedRawThreadInfos,
   NewThreadResult,
@@ -1515,7 +1514,7 @@
 
 function removeMemberFromThread(
   threadInfo: ThreadInfo,
-  memberInfo: LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
+  memberInfo: MinimallyEncodedRelativeMemberInfo,
   dispatchActionPromise: DispatchActionPromise,
   removeUserFromThreadServerCall: (
     input: RemoveUsersFromThreadInput,
@@ -1533,7 +1532,7 @@
 }
 
 function getAvailableThreadMemberActions(
-  memberInfo: LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
+  memberInfo: MinimallyEncodedRelativeMemberInfo,
   threadInfo: ThreadInfo,
   canEdit: ?boolean = true,
 ): $ReadOnlyArray<'change_role' | 'remove_user'> {
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
@@ -54,12 +54,6 @@
 
 export type MemberInfo = LegacyMemberInfo | MinimallyEncodedMemberInfo;
 
-export type LegacyRelativeMemberInfo = $ReadOnly<{
-  ...LegacyMemberInfo,
-  +username: ?string,
-  +isViewer: boolean,
-}>;
-
 export type LegacyRoleInfo = {
   +id: string,
   +name: string,
diff --git a/lib/utils/role-utils.js b/lib/utils/role-utils.js
--- a/lib/utils/role-utils.js
+++ b/lib/utils/role-utils.js
@@ -13,7 +13,7 @@
   type ThreadRolePermissionsBlob,
   type UserSurfacedPermission,
 } from '../types/thread-permission-types.js';
-import type { LegacyRelativeMemberInfo, RoleInfo } from '../types/thread-types';
+import type { RoleInfo } from '../types/thread-types';
 import { threadTypes } from '../types/thread-types-enum.js';
 
 function constructRoleDeletionMessagePrompt(
@@ -57,9 +57,7 @@
 
 function useRolesFromCommunityThreadInfo(
   threadInfo: ThreadInfo,
-  memberInfos: $ReadOnlyArray<
-    LegacyRelativeMemberInfo | MinimallyEncodedRelativeMemberInfo,
-  >,
+  memberInfos: $ReadOnlyArray<MinimallyEncodedRelativeMemberInfo>,
 ): $ReadOnlyMap<string, ?RoleInfo> {
   // Our in-code system has chat-specific roles, while the
   // user-surfaced system has roles only for communities. We retrieve roles