diff --git a/lib/shared/message-utils.js b/lib/shared/message-utils.js
--- a/lib/shared/message-utils.js
+++ b/lib/shared/message-utils.js
@@ -43,13 +43,10 @@
   ReactionMessageInfo,
 } from '../types/messages/reaction.js';
 import type {
-  ThreadInfo,
   RawThreadInfo,
+  ThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
-import type {
-  LegacyRawThreadInfo,
-  LegacyThreadInfo,
-} from '../types/thread-types.js';
+import type { LegacyRawThreadInfo } from '../types/thread-types.js';
 import type { UserInfos } from '../types/user-types.js';
 import {
   type EntityText,
@@ -82,8 +79,8 @@
 
 function robotextForMessageInfo(
   messageInfo: RobotextMessageInfo,
-  threadInfo: ?LegacyThreadInfo | ?ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ?ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
 ): EntityText {
   const messageSpec = messageSpecs[messageInfo.type];
   invariant(
@@ -97,7 +94,7 @@
   rawMessageInfo: RawMessageInfo,
   viewerID: ?string,
   userInfos: UserInfos,
-  threadInfos: { +[id: string]: LegacyThreadInfo | ThreadInfo },
+  threadInfos: { +[id: string]: ThreadInfo },
 ): ?MessageInfo {
   const creatorInfo = userInfos[rawMessageInfo.creatorID];
   const creator = {
@@ -418,8 +415,8 @@
     | RobotextMessageInfo
     | ReactionMessageInfo
     | EditMessageInfo,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
   markdownRules: ParserRules,
 ): EntityText {
   const { messageTitle } = messageSpecs[messageInfo.type];
@@ -505,7 +502,7 @@
 };
 function useMessagePreview(
   originalMessageInfo: ?MessageInfo,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   markdownRules: ParserRules,
 ): ?MessagePreviewResult {
   let messageInfo;
@@ -687,11 +684,7 @@
 
 function isInvalidPinSourceForThread(
   messageInfo: RawMessageInfo | MessageInfo,
-  threadInfo:
-    | LegacyRawThreadInfo
-    | RawThreadInfo
-    | LegacyThreadInfo
-    | ThreadInfo,
+  threadInfo: LegacyRawThreadInfo | RawThreadInfo | ThreadInfo,
 ): boolean {
   const isValidPinSource = !isInvalidPinSource(messageInfo);
   const isFirstMessageInSidebar = threadInfo.sourceMessageID === messageInfo.id;
diff --git a/lib/shared/messages/add-members-message-spec.js b/lib/shared/messages/add-members-message-spec.js
--- a/lib/shared/messages/add-members-message-spec.js
+++ b/lib/shared/messages/add-members-message-spec.js
@@ -21,7 +21,6 @@
 } from '../../types/messages/add-members.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -125,7 +124,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
     params: NotificationTextsParams,
   ): Promise<NotifTexts> {
     const addedMembersObject: { [string]: RelativeUserInfo } = {};
diff --git a/lib/shared/messages/change-role-message-spec.js b/lib/shared/messages/change-role-message-spec.js
--- a/lib/shared/messages/change-role-message-spec.js
+++ b/lib/shared/messages/change-role-message-spec.js
@@ -25,7 +25,6 @@
 import type { RawUnsupportedMessageInfo } from '../../types/messages/unsupported';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -159,7 +158,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
     params: NotificationTextsParams,
   ): Promise<NotifTexts> {
     const membersObject: { [string]: RelativeUserInfo } = {};
diff --git a/lib/shared/messages/change-settings-message-spec.js b/lib/shared/messages/change-settings-message-spec.js
--- a/lib/shared/messages/change-settings-message-spec.js
+++ b/lib/shared/messages/change-settings-message-spec.js
@@ -23,7 +23,6 @@
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
 import { assertThreadType } from '../../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
 import { validHexColorRegex } from '../account-utils.js';
@@ -159,7 +158,7 @@
 
     async notificationTexts(
       messageInfos: $ReadOnlyArray<MessageInfo>,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
+      threadInfo: ThreadInfo,
       params: NotificationTextsParams,
     ): Promise<NotifTexts> {
       const mostRecentMessageInfo = messageInfos[0];
diff --git a/lib/shared/messages/create-entry-message-spec.js b/lib/shared/messages/create-entry-message-spec.js
--- a/lib/shared/messages/create-entry-message-spec.js
+++ b/lib/shared/messages/create-entry-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/create-entry.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { prettyDate } from '../../utils/date-utils.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
@@ -120,7 +119,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     return notifTextsForEntryCreationOrEdit(messageInfos, threadInfo);
   },
diff --git a/lib/shared/messages/create-sidebar-message-spec.js b/lib/shared/messages/create-sidebar-message-spec.js
--- a/lib/shared/messages/create-sidebar-message-spec.js
+++ b/lib/shared/messages/create-sidebar-message-spec.js
@@ -23,7 +23,6 @@
 } from '../../types/messages/create-sidebar.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -174,7 +173,7 @@
 
     async notificationTexts(
       messageInfos: $ReadOnlyArray<MessageInfo>,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
+      threadInfo: ThreadInfo,
       params: NotificationTextsParams,
     ): Promise<NotifTexts> {
       const createSidebarMessageInfo = messageInfos[0];
diff --git a/lib/shared/messages/create-sub-thread-message-spec.js b/lib/shared/messages/create-sub-thread-message-spec.js
--- a/lib/shared/messages/create-sub-thread-message-spec.js
+++ b/lib/shared/messages/create-sub-thread-message-spec.js
@@ -25,7 +25,6 @@
 import type { NotifTexts } from '../../types/notif-types.js';
 import { threadPermissions } from '../../types/thread-permission-types.js';
 import { threadTypes } from '../../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
 import { notifTextsForSubthreadCreation } from '../notif-utils.js';
@@ -141,7 +140,7 @@
 
     async notificationTexts(
       messageInfos: $ReadOnlyArray<MessageInfo>,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
+      threadInfo: ThreadInfo,
     ): Promise<NotifTexts> {
       const messageInfo = assertSingleMessageInfo(messageInfos);
       invariant(
diff --git a/lib/shared/messages/create-thread-message-spec.js b/lib/shared/messages/create-thread-message-spec.js
--- a/lib/shared/messages/create-thread-message-spec.js
+++ b/lib/shared/messages/create-thread-message-spec.js
@@ -22,7 +22,6 @@
 } from '../../types/messages/create-thread.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -158,7 +157,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
diff --git a/lib/shared/messages/delete-entry-message-spec.js b/lib/shared/messages/delete-entry-message-spec.js
--- a/lib/shared/messages/delete-entry-message-spec.js
+++ b/lib/shared/messages/delete-entry-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/delete-entry.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { prettyDate } from '../../utils/date-utils.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
@@ -119,7 +118,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
diff --git a/lib/shared/messages/edit-entry-message-spec.js b/lib/shared/messages/edit-entry-message-spec.js
--- a/lib/shared/messages/edit-entry-message-spec.js
+++ b/lib/shared/messages/edit-entry-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/edit-entry.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { prettyDate } from '../../utils/date-utils.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
@@ -120,7 +119,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     return notifTextsForEntryCreationOrEdit(messageInfos, threadInfo);
   },
diff --git a/lib/shared/messages/join-thread-message-spec.js b/lib/shared/messages/join-thread-message-spec.js
--- a/lib/shared/messages/join-thread-message-spec.js
+++ b/lib/shared/messages/join-thread-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/join-thread.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -90,7 +89,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const joinerArray: { [string]: RelativeUserInfo } = {};
     for (const messageInfo of messageInfos) {
diff --git a/lib/shared/messages/leave-thread-message-spec.js b/lib/shared/messages/leave-thread-message-spec.js
--- a/lib/shared/messages/leave-thread-message-spec.js
+++ b/lib/shared/messages/leave-thread-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/leave-thread.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -90,7 +89,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const leaverBeavers: { [string]: RelativeUserInfo } = {};
     for (const messageInfo of messageInfos) {
diff --git a/lib/shared/messages/message-spec.js b/lib/shared/messages/message-spec.js
--- a/lib/shared/messages/message-spec.js
+++ b/lib/shared/messages/message-spec.js
@@ -14,14 +14,13 @@
 import type { RawUnsupportedMessageInfo } from '../../types/messages/unsupported.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo, UserInfo } from '../../types/user-types.js';
 import type { EntityText } from '../../utils/entity-text.js';
 import { type ParserRules } from '../markdown.js';
 
 export type MessageTitleParam<Info> = {
   +messageInfo: Info,
-  +threadInfo: LegacyThreadInfo | ThreadInfo,
+  +threadInfo: ThreadInfo,
   +markdownRules: ParserRules,
 };
 
@@ -36,7 +35,7 @@
 
 export type CreateMessageInfoParams = {
   +threadInfos: {
-    +[id: string]: LegacyThreadInfo | ThreadInfo,
+    +[id: string]: ThreadInfo,
   },
   +createMessageInfoFromRaw: (rawInfo: RawMessageInfo) => ?MessageInfo,
   +createRelativeUserInfos: (
@@ -45,13 +44,13 @@
 };
 
 export type RobotextParams = {
-  +threadInfo: ?LegacyThreadInfo | ?ThreadInfo,
-  +parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  +threadInfo: ?ThreadInfo,
+  +parentThreadInfo: ?ThreadInfo,
 };
 
 export type NotificationTextsParams = {
   +notifTargetUserInfo: UserInfo,
-  +parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  +parentThreadInfo: ?ThreadInfo,
 };
 
 export type GeneratesNotifsParams = {
@@ -68,8 +67,8 @@
 
 export type CreationSideEffectsFunc<RawInfo> = (
   messageInfo: RawInfo,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
 ) => Promise<mixed>;
 
 export type MessageSpec<Data, RawInfo, Info> = {
@@ -100,7 +99,7 @@
   ) => ?RawMessageInfo,
   +notificationTexts?: (
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
     params: NotificationTextsParams,
   ) => Promise<?NotifTexts>,
   +notificationCollapseKey?: (
diff --git a/lib/shared/messages/multimedia-message-spec.js b/lib/shared/messages/multimedia-message-spec.js
--- a/lib/shared/messages/multimedia-message-spec.js
+++ b/lib/shared/messages/multimedia-message-spec.js
@@ -43,7 +43,6 @@
 import type { RawUnsupportedMessageInfo } from '../../types/messages/unsupported.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { ET } from '../../utils/entity-text.js';
 import {
@@ -312,7 +311,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const media = [];
     for (const messageInfo of messageInfos) {
diff --git a/lib/shared/messages/reaction-message-spec.js b/lib/shared/messages/reaction-message-spec.js
--- a/lib/shared/messages/reaction-message-spec.js
+++ b/lib/shared/messages/reaction-message-spec.js
@@ -27,7 +27,6 @@
 import type { RawUnsupportedMessageInfo } from '../../types/messages/unsupported.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { ET } from '../../utils/entity-text.js';
 import { threadIsGroupChat } from '../thread-utils.js';
@@ -164,7 +163,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
diff --git a/lib/shared/messages/remove-members-message-spec.js b/lib/shared/messages/remove-members-message-spec.js
--- a/lib/shared/messages/remove-members-message-spec.js
+++ b/lib/shared/messages/remove-members-message-spec.js
@@ -21,7 +21,6 @@
 } from '../../types/messages/remove-members.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import {
   type EntityText,
@@ -126,7 +125,7 @@
 
     async notificationTexts(
       messageInfos: $ReadOnlyArray<MessageInfo>,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
+      threadInfo: ThreadInfo,
       params: NotificationTextsParams,
     ): Promise<NotifTexts> {
       const removedMembersObject: { [string]: RelativeUserInfo } = {};
diff --git a/lib/shared/messages/restore-entry-message-spec.js b/lib/shared/messages/restore-entry-message-spec.js
--- a/lib/shared/messages/restore-entry-message-spec.js
+++ b/lib/shared/messages/restore-entry-message-spec.js
@@ -17,7 +17,6 @@
 } from '../../types/messages/restore-entry.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { prettyDate } from '../../utils/date-utils.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
@@ -119,7 +118,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ): Promise<NotifTexts> {
     const messageInfo = assertSingleMessageInfo(messageInfos);
     invariant(
diff --git a/lib/shared/messages/text-message-spec.js b/lib/shared/messages/text-message-spec.js
--- a/lib/shared/messages/text-message-spec.js
+++ b/lib/shared/messages/text-message-spec.js
@@ -28,7 +28,6 @@
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
 import { threadTypes } from '../../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { ET } from '../../utils/entity-text.js';
 import { useDispatchActionPromise } from '../../utils/redux-promise-utils.js';
@@ -199,7 +198,7 @@
 
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
     params: NotificationTextsParams,
   ): Promise<?NotifTexts> {
     // We special-case sidebarCreations. Usually we don't send any notifs in
@@ -295,8 +294,8 @@
     const callChangeThreadSettings = useChangeThreadSettings();
     return async (
       messageInfo: RawTextMessageInfo,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
-      parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+      threadInfo: ThreadInfo,
+      parentThreadInfo: ?ThreadInfo,
     ) => {
       if (threadInfo.type !== threadTypes.SIDEBAR) {
         return;
diff --git a/lib/shared/messages/update-relationship-message-spec.js b/lib/shared/messages/update-relationship-message-spec.js
--- a/lib/shared/messages/update-relationship-message-spec.js
+++ b/lib/shared/messages/update-relationship-message-spec.js
@@ -21,7 +21,6 @@
 } from '../../types/messages/update-relationship.js';
 import type { ThreadInfo } from '../../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts } from '../../types/notif-types.js';
-import type { LegacyThreadInfo } from '../../types/thread-types.js';
 import type { RelativeUserInfo } from '../../types/user-types.js';
 import { type EntityText, ET } from '../../utils/entity-text.js';
 
@@ -149,7 +148,7 @@
 
     async notificationTexts(
       messageInfos: $ReadOnlyArray<MessageInfo>,
-      threadInfo: LegacyThreadInfo | ThreadInfo,
+      threadInfo: ThreadInfo,
     ): Promise<NotifTexts> {
       const messageInfo = assertSingleMessageInfo(messageInfos);
       const creator = ET.user({ userInfo: messageInfo.creator });
diff --git a/lib/shared/notif-utils.js b/lib/shared/notif-utils.js
--- a/lib/shared/notif-utils.js
+++ b/lib/shared/notif-utils.js
@@ -20,7 +20,6 @@
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import type { NotifTexts, ResolvedNotifTexts } from '../types/notif-types.js';
 import { type ThreadType, threadTypes } from '../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import type { RelativeUserInfo, UserInfo } from '../types/user-types.js';
 import { prettyDate } from '../utils/date-utils.js';
 import type { GetENSNames } from '../utils/ens-helpers.js';
@@ -35,8 +34,8 @@
 
 async function notifTextsForMessageInfo(
   messageInfos: MessageInfo[],
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
   notifTargetUserInfo: UserInfo,
   getENSNames: ?GetENSNames,
 ): Promise<?ResolvedNotifTexts> {
@@ -62,7 +61,7 @@
 
 function notifTextsForEntryCreationOrEdit(
   messageInfos: $ReadOnlyArray<MessageInfo>,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): NotifTexts {
   const hasCreateEntry = messageInfos.some(
     messageInfo => messageInfo.type === messageTypes.CREATE_ENTRY,
@@ -109,7 +108,7 @@
 type NotifTextsForSubthreadCreationInput = {
   +creator: RelativeUserInfo,
   +threadType: ThreadType,
-  +parentThreadInfo: LegacyThreadInfo | ThreadInfo,
+  +parentThreadInfo: ThreadInfo,
   +childThreadName: ?string,
   +childThreadUIName: string | ThreadEntity,
 };
@@ -151,7 +150,7 @@
   +createSidebarMessageInfo: CreateSidebarMessageInfo,
   +sidebarSourceMessageInfo?: ?SidebarSourceMessageInfo,
   +firstSidebarMessageInfo?: ?TextMessageInfo,
-  +threadInfo: LegacyThreadInfo | ThreadInfo,
+  +threadInfo: ThreadInfo,
   +params: NotificationTextsParams,
 };
 function notifTextsForSidebarCreation(
@@ -215,8 +214,8 @@
 
 async function fullNotifTextsForMessageInfo(
   messageInfos: $ReadOnlyArray<MessageInfo>,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
   notifTargetUserInfo: UserInfo,
   getENSNames: ?GetENSNames,
 ): Promise<?ResolvedNotifTexts> {
@@ -266,8 +265,8 @@
 
 function notifRobotextForMessageInfo(
   messageInfo: RobotextMessageInfo,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
 ): EntityText {
   const robotext = robotextForMessageInfo(
     messageInfo,
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
@@ -244,7 +244,7 @@
   );
 }
 
-function threadIsGroupChat(threadInfo: LegacyThreadInfo | ThreadInfo): boolean {
+function threadIsGroupChat(threadInfo: ThreadInfo): boolean {
   return threadInfo.members.length > 2;
 }
 
@@ -325,7 +325,7 @@
   +viewerID: string,
   +threadType: ThreadType,
   +members: $ReadOnlyArray<UserIDAndUsername>,
-  +parentThreadInfo?: ?(LegacyThreadInfo | ThreadInfo),
+  +parentThreadInfo?: ?ThreadInfo,
   +threadColor?: ?string,
   +name?: ?string,
   +sourceMessageID?: string,
@@ -470,7 +470,7 @@
 // Returns map from user ID to AccountUserInfo
 function extractMentionedMembers(
   text: string,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): Map<string, AccountUserInfo> {
   const memberMap = memberLowercaseUsernameMap(threadInfo.members);
   const mentions = extractUserMentionsFromText(text);
@@ -489,8 +489,8 @@
 // they will be automatically added to that sidebar
 function extractNewMentionedParentMembers(
   messageText: string,
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ThreadInfo,
 ): AccountUserInfo[] {
   const mentionedMembersOfParent = extractMentionedMembers(
     messageText,
@@ -678,7 +678,7 @@
 }
 
 type CreateRealThreadParameters = {
-  +threadInfo: LegacyThreadInfo | ThreadInfo,
+  +threadInfo: ThreadInfo,
   +dispatchActionPromise: DispatchActionPromise,
   +createNewThread: ClientNewThreadRequest => Promise<NewThreadResult>,
   +sourceMessageID: ?string,
@@ -1427,7 +1427,6 @@
     | ?ServerThreadInfo
     | LegacyRawThreadInfo
     | RawThreadInfo
-    | LegacyThreadInfo
     | ThreadInfo,
   threadType: ThreadType,
 ): ?string {
@@ -1448,7 +1447,6 @@
     | ?ServerThreadInfo
     | LegacyRawThreadInfo
     | RawThreadInfo
-    | LegacyThreadInfo
     | ThreadInfo,
 ): ?string {
   if (!parentThreadInfo) {
@@ -1689,7 +1687,7 @@
 // the set of permission literals for each role to user-facing permission enums
 // to help pre-populate the permission checkboxes when editing roles.
 function useRoleUserSurfacedPermissions(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): RoleUserSurfacedPermissions {
   return React.useMemo(() => {
     const roleNamesToPermissions: { [string]: Set<UserSurfacedPermission> } =
diff --git a/lib/types/messages/create-sidebar.js b/lib/types/messages/create-sidebar.js
--- a/lib/types/messages/create-sidebar.js
+++ b/lib/types/messages/create-sidebar.js
@@ -5,7 +5,6 @@
 import { tID, tNumber, tShape } from '../../utils/validation-utils.js';
 import { messageTypes } from '../message-types-enum.js';
 import type { ThreadInfo } from '../minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo } from '../thread-types.js';
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type CreateSidebarMessageData = {
@@ -52,7 +51,7 @@
   +sourceMessageAuthor: RelativeUserInfo,
   +initialThreadState: {
     +name: ?string,
-    +parentThreadInfo: LegacyThreadInfo | ThreadInfo,
+    +parentThreadInfo: ThreadInfo,
     +color: string,
     +otherMembers: RelativeUserInfo[],
   },
diff --git a/lib/types/messages/create-subthread.js b/lib/types/messages/create-subthread.js
--- a/lib/types/messages/create-subthread.js
+++ b/lib/types/messages/create-subthread.js
@@ -5,7 +5,6 @@
 import { tID, tNumber, tShape } from '../../utils/validation-utils.js';
 import { messageTypes } from '../message-types-enum.js';
 import type { ThreadInfo } from '../minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo } from '../thread-types.js';
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type CreateSubthreadMessageData = {
@@ -37,5 +36,5 @@
   threadID: string,
   creator: RelativeUserInfo,
   time: number,
-  childThreadInfo: LegacyThreadInfo | ThreadInfo,
+  childThreadInfo: ThreadInfo,
 };
diff --git a/lib/types/messages/create-thread.js b/lib/types/messages/create-thread.js
--- a/lib/types/messages/create-thread.js
+++ b/lib/types/messages/create-thread.js
@@ -12,7 +12,6 @@
 import { messageTypes } from '../message-types-enum.js';
 import type { ThreadInfo } from '../minimally-encoded-thread-permissions-types.js';
 import { type ThreadType, threadTypes } from '../thread-types-enum.js';
-import type { LegacyThreadInfo } from '../thread-types.js';
 import type { RelativeUserInfo } from '../user-types.js';
 
 export type CreateThreadMessageData = {
@@ -59,7 +58,7 @@
   initialThreadState: {
     type: ThreadType,
     name: ?string,
-    parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+    parentThreadInfo: ?ThreadInfo,
     color: string,
     otherMembers: RelativeUserInfo[],
   },
diff --git a/lib/utils/entity-text.js b/lib/utils/entity-text.js
--- a/lib/utils/entity-text.js
+++ b/lib/utils/entity-text.js
@@ -10,18 +10,15 @@
 import { threadNoun } from '../shared/thread-utils.js';
 import { stringForUser } from '../shared/user-utils.js';
 import type {
-  ThreadInfo,
   RawThreadInfo,
+  ThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import {
   type ThreadType,
   threadTypes,
   threadTypeValidator,
 } from '../types/thread-types-enum.js';
-import type {
-  LegacyRawThreadInfo,
-  LegacyThreadInfo,
-} from '../types/thread-types.js';
+import type { LegacyRawThreadInfo } from '../types/thread-types.js';
 import { basePluralize } from '../utils/text-utils.js';
 
 export type UserEntity = {
@@ -141,25 +138,17 @@
 type EntityTextThreadInput =
   | {
       +display: 'uiName',
-      +threadInfo: LegacyThreadInfo | ThreadInfo,
+      +threadInfo: ThreadInfo,
     }
   | {
       +display?: 'shortName',
-      +threadInfo:
-        | LegacyRawThreadInfo
-        | RawThreadInfo
-        | LegacyThreadInfo
-        | ThreadInfo,
+      +threadInfo: LegacyRawThreadInfo | RawThreadInfo | ThreadInfo,
       +subchannel?: ?boolean,
       +possessive?: ?boolean,
     }
   | {
       +display: 'alwaysDisplayShortName',
-      +threadInfo:
-        | LegacyRawThreadInfo
-        | RawThreadInfo
-        | LegacyThreadInfo
-        | ThreadInfo,
+      +threadInfo: LegacyRawThreadInfo | RawThreadInfo | ThreadInfo,
       +possessive?: ?boolean,
     }
   | {