diff --git a/lib/components/chat-mention-provider.react.js b/lib/components/chat-mention-provider.react.js
--- a/lib/components/chat-mention-provider.react.js
+++ b/lib/components/chat-mention-provider.react.js
@@ -13,7 +13,6 @@
 import type {
   ChatMentionCandidate,
   ChatMentionCandidatesObj,
-  LegacyThreadInfo,
 } from '../types/thread-types.js';
 import { useResolvedThreadInfosObj } from '../utils/entity-helpers.js';
 import { getNameForThreadEntity } from '../utils/entity-text.js';
@@ -24,7 +23,7 @@
 };
 export type ChatMentionContextType = {
   +getChatMentionSearchIndex: (
-    threadInfo: LegacyThreadInfo | ThreadInfo,
+    threadInfo: ThreadInfo,
   ) => SentencePrefixSearchIndex,
   +communityThreadIDForGenesisThreads: { +[id: string]: string },
   +chatMentionCandidatesObj: ChatMentionCandidatesObj,
@@ -46,7 +45,7 @@
   const searchIndices = useChatMentionSearchIndex(chatMentionCandidatesObj);
 
   const getChatMentionSearchIndex = React.useCallback(
-    (threadInfo: LegacyThreadInfo | ThreadInfo) => {
+    (threadInfo: ThreadInfo) => {
       if (threadInfo.community === genesis.id) {
         return searchIndices[communityThreadIDForGenesisThreads[threadInfo.id]];
       }
diff --git a/lib/hooks/chat-mention-hooks.js b/lib/hooks/chat-mention-hooks.js
--- a/lib/hooks/chat-mention-hooks.js
+++ b/lib/hooks/chat-mention-hooks.js
@@ -9,10 +9,7 @@
 } from '../components/chat-mention-provider.react.js';
 import genesis from '../facts/genesis.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
-import type {
-  ChatMentionCandidates,
-  LegacyThreadInfo,
-} from '../types/thread-types.js';
+import type { ChatMentionCandidates } from '../types/thread-types.js';
 
 function useChatMentionContext(): ChatMentionContextType {
   const context = React.useContext(ChatMentionContext);
@@ -22,7 +19,7 @@
 }
 
 function useThreadChatMentionCandidates(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): ChatMentionCandidates {
   const { communityThreadIDForGenesisThreads, chatMentionCandidatesObj } =
     useChatMentionContext();
diff --git a/lib/hooks/child-threads.js b/lib/hooks/child-threads.js
--- a/lib/hooks/child-threads.js
+++ b/lib/hooks/child-threads.js
@@ -18,12 +18,11 @@
   ThreadInfo,
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
 import { useSelector } from '../utils/redux-utils.js';
 
 type ThreadFilter = {
-  +predicate?: (thread: LegacyThreadInfo | ThreadInfo) => boolean,
+  +predicate?: (thread: ThreadInfo) => boolean,
   +searchText?: string,
 };
 
@@ -44,7 +43,7 @@
   }, [childThreads, predicate]);
 
   const filterSubchannels = React.useCallback(
-    (thread: ?(RawThreadInfo | LegacyThreadInfo | ThreadInfo)) => {
+    (thread: ?(RawThreadInfo | ThreadInfo)) => {
       const candidateThreadID = thread?.id;
       if (!candidateThreadID) {
         return false;
diff --git a/lib/hooks/promote-sidebar.react.js b/lib/hooks/promote-sidebar.react.js
--- a/lib/hooks/promote-sidebar.react.js
+++ b/lib/hooks/promote-sidebar.react.js
@@ -16,13 +16,12 @@
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-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 { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
 import { useSelector } from '../utils/redux-utils.js';
 
 function canPromoteSidebar(
-  sidebarThreadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  sidebarThreadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
 ): boolean {
   if (!threadIsSidebar(sidebarThreadInfo)) {
     return false;
@@ -46,7 +45,7 @@
 };
 
 function usePromoteSidebar(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   onError?: () => mixed,
 ): PromoteSidebarType {
   const dispatchActionPromise = useDispatchActionPromise();
@@ -57,9 +56,8 @@
   const loadingStatus = useSelector(loadingStatusSelector);
 
   const { parentThreadID } = threadInfo;
-  const parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo = useSelector(
-    state =>
-      parentThreadID ? threadInfoSelector(state)[parentThreadID] : null,
+  const parentThreadInfo: ?ThreadInfo = useSelector(state =>
+    parentThreadID ? threadInfoSelector(state)[parentThreadID] : null,
   );
 
   const canPromote = canPromoteSidebar(threadInfo, parentThreadInfo);
diff --git a/lib/hooks/relationship-prompt.js b/lib/hooks/relationship-prompt.js
--- a/lib/hooks/relationship-prompt.js
+++ b/lib/hooks/relationship-prompt.js
@@ -13,7 +13,6 @@
   type RelationshipAction,
   relationshipActions,
 } from '../types/relationship-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import type { UserInfo } from '../types/user-types.js';
 import { useLegacyAshoatKeyserverCall } from '../utils/action-utils.js';
 import { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
@@ -32,7 +31,7 @@
 };
 
 function useRelationshipPrompt(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   onErrorCallback?: () => void,
   pendingPersonalThreadUserInfo?: ?UserInfo,
 ): RelationshipPromptData {
diff --git a/lib/hooks/search-threads.js b/lib/hooks/search-threads.js
--- a/lib/hooks/search-threads.js
+++ b/lib/hooks/search-threads.js
@@ -14,7 +14,7 @@
   ThreadInfo,
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo, SidebarInfo } from '../types/thread-types.js';
+import type { SidebarInfo } from '../types/thread-types.js';
 import { useSelector } from '../utils/redux-utils.js';
 
 export type ThreadSearchState = {
@@ -31,7 +31,7 @@
 };
 
 function useSearchThreads<U: SidebarInfo | ChatThreadItem>(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   childThreadInfos: $ReadOnlyArray<U>,
 ): SearchThreadsResult<U> {
   const [searchState, setSearchState] = React.useState<ThreadSearchState>({
@@ -91,7 +91,7 @@
 }
 
 function useSearchSidebars(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): SearchThreadsResult<SidebarInfo> {
   const childThreadInfos = useSelector(
     state => sidebarInfoSelector(state)[threadInfo.id] ?? [],
@@ -100,10 +100,10 @@
 }
 
 function useSearchSubchannels(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
 ): SearchThreadsResult<ChatThreadItem> {
   const filterFunc = React.useCallback(
-    (thread: ?(LegacyThreadInfo | ThreadInfo | RawThreadInfo)) =>
+    (thread: ?(ThreadInfo | RawThreadInfo)) =>
       threadIsChannel(thread) && thread?.parentThreadID === threadInfo.id,
     [threadInfo.id],
   );
diff --git a/lib/hooks/toggle-unread-status.js b/lib/hooks/toggle-unread-status.js
--- a/lib/hooks/toggle-unread-status.js
+++ b/lib/hooks/toggle-unread-status.js
@@ -11,11 +11,10 @@
   SetThreadUnreadStatusRequest,
 } from '../types/activity-types.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
 
 function useToggleUnreadStatus(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   mostRecentNonLocalMessage: ?string,
   afterAction: () => void,
 ): () => void {
diff --git a/lib/selectors/chat-selectors.js b/lib/selectors/chat-selectors.js
--- a/lib/selectors/chat-selectors.js
+++ b/lib/selectors/chat-selectors.js
@@ -45,7 +45,6 @@
   maxReadSidebars,
   maxUnreadSidebars,
   type SidebarInfo,
-  type LegacyThreadInfo,
 } from '../types/thread-types.js';
 import type {
   AccountUserInfo,
@@ -98,7 +97,7 @@
 }
 
 function getMostRecentMessageInfo(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   messageStore: MessageStore,
   messages: { +[id: string]: ?MessageInfo },
 ): ?MessageInfo {
@@ -117,7 +116,7 @@
 }
 
 function getLastUpdatedTime(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   mostRecentMessageInfo: ?MessageInfo,
 ): number {
   return mostRecentMessageInfo
@@ -232,9 +231,7 @@
 }
 
 function useFilteredChatListData(
-  filterFunction: (
-    threadInfo: ?(LegacyThreadInfo | ThreadInfo | RawThreadInfo),
-  ) => boolean,
+  filterFunction: (threadInfo: ?(ThreadInfo | RawThreadInfo)) => boolean,
 ): $ReadOnlyArray<ChatThreadItem> {
   const threadInfos = useSelector(threadInfoSelector);
   const messageInfos = useSelector(messageInfoSelector);
@@ -620,7 +617,7 @@
 export type UseMessageListDataArgs = {
   +searching: boolean,
   +userInfoInputArray: $ReadOnlyArray<AccountUserInfo>,
-  +threadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  +threadInfo: ?ThreadInfo,
 };
 
 function useMessageListData({
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
@@ -18,10 +18,7 @@
 } 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 {
-  LegacyThreadInfo,
-  RelativeMemberInfo,
-} from '../types/thread-types';
+import type { RelativeMemberInfo } from '../types/thread-types';
 import type { UserInfo } from '../types/user-types.js';
 import { getConfig } from '../utils/config.js';
 import { values } from '../utils/objects.js';
@@ -123,7 +120,7 @@
 }
 
 function useThreadSearchIndex(
-  threadInfos: $ReadOnlyArray<RawThreadInfo | LegacyThreadInfo | ThreadInfo>,
+  threadInfos: $ReadOnlyArray<RawThreadInfo | ThreadInfo>,
 ): SearchIndex {
   const userInfos = useSelector(state => state.userStore.userInfos);
   const viewerID = useSelector(
diff --git a/lib/shared/avatar-utils.js b/lib/shared/avatar-utils.js
--- a/lib/shared/avatar-utils.js
+++ b/lib/shared/avatar-utils.js
@@ -21,10 +21,7 @@
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadTypes } from '../types/thread-types-enum.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 { useSelector } from '../utils/redux-utils.js';
 import { ashoatKeyserverID } from '../utils/validation-utils.js';
@@ -277,11 +274,7 @@
 }
 
 function getUserAvatarForThread(
-  threadInfo:
-    | LegacyRawThreadInfo
-    | RawThreadInfo
-    | LegacyThreadInfo
-    | ThreadInfo,
+  threadInfo: LegacyRawThreadInfo | RawThreadInfo | ThreadInfo,
   viewerID: ?string,
   userInfos: UserInfos,
 ): ClientAvatar {
@@ -307,8 +300,8 @@
 }
 
 function getAvatarForThread(
-  thread: RawThreadInfo | LegacyThreadInfo | ThreadInfo,
-  containingThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  thread: RawThreadInfo | ThreadInfo,
+  containingThreadInfo: ?ThreadInfo,
 ): ClientAvatar {
   if (thread.avatar) {
     return thread.avatar;
@@ -323,9 +316,7 @@
   return getDefaultAvatar(thread.id, thread.color);
 }
 
-function useAvatarForThread(
-  thread: RawThreadInfo | LegacyThreadInfo | ThreadInfo,
-): ClientAvatar {
+function useAvatarForThread(thread: RawThreadInfo | ThreadInfo): ClientAvatar {
   const containingThreadID = thread.containingThreadID;
   const containingThreadInfo = useSelector(state =>
     containingThreadID ? threadInfoSelector(state)[containingThreadID] : null,
diff --git a/lib/shared/edit-messages-utils.js b/lib/shared/edit-messages-utils.js
--- a/lib/shared/edit-messages-utils.js
+++ b/lib/shared/edit-messages-utils.js
@@ -16,7 +16,6 @@
 import { messageTypes } from '../types/message-types-enum.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
 import { useSelector } from '../utils/redux-utils.js';
 
@@ -52,7 +51,7 @@
 }
 
 function useCanEditMessage(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   targetMessageInfo: ComposableMessageInfo | RobotextMessageInfo,
 ): boolean {
   const currentUserInfo = useSelector(state => state.currentUserInfo);
diff --git a/lib/shared/inline-engagement-utils.js b/lib/shared/inline-engagement-utils.js
--- a/lib/shared/inline-engagement-utils.js
+++ b/lib/shared/inline-engagement-utils.js
@@ -2,11 +2,8 @@
 
 import type { ReactionInfo } from '../selectors/chat-selectors.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 
-function getInlineEngagementSidebarText(
-  threadInfo: ?LegacyThreadInfo | ?ThreadInfo,
-): string {
+function getInlineEngagementSidebarText(threadInfo: ?ThreadInfo): string {
   if (!threadInfo) {
     return '';
   }
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
@@ -14,7 +14,6 @@
 import { threadTypes } from '../types/thread-types-enum.js';
 import type {
   ChatMentionCandidates,
-  LegacyThreadInfo,
   RelativeMemberInfo,
 } from '../types/thread-types.js';
 import { chatNameMaxLength, idSchemaRegex } from '../utils/validation-utils.js';
@@ -185,8 +184,8 @@
 }
 
 function useUserMentionsCandidates(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
-  parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  threadInfo: ThreadInfo,
+  parentThreadInfo: ?ThreadInfo,
 ): $ReadOnlyArray<RelativeMemberInfo> {
   return React.useMemo(() => {
     if (threadInfo.type !== threadTypes.SIDEBAR) {
diff --git a/lib/shared/reaction-utils.js b/lib/shared/reaction-utils.js
--- a/lib/shared/reaction-utils.js
+++ b/lib/shared/reaction-utils.js
@@ -14,7 +14,6 @@
 } from '../types/message-types.js';
 import type { ThreadInfo } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import { useSelector } from '../utils/redux-utils.js';
 
 function useViewerAlreadySelectedMessageReactions(
@@ -75,7 +74,7 @@
 }
 
 function useCanCreateReactionFromMessage(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   targetMessageInfo: ComposableMessageInfo | RobotextMessageInfo,
 ): boolean {
   const targetMessageCreatorRelationship = useSelector(
diff --git a/lib/shared/search-utils.js b/lib/shared/search-utils.js
--- a/lib/shared/search-utils.js
+++ b/lib/shared/search-utils.js
@@ -30,7 +30,6 @@
 import { userRelationshipStatus } from '../types/relationship-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
 import { type ThreadType, threadTypes } from '../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 import type {
   AccountUserInfo,
   GlobalAccountUserInfo,
@@ -61,9 +60,9 @@
   },
   +excludeUserIDs: $ReadOnlyArray<string>,
   +userInfo: AccountUserInfo | GlobalAccountUserInfo,
-  +parentThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
-  +communityThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
-  +containingThreadInfo: ?LegacyThreadInfo | ?ThreadInfo,
+  +parentThreadInfo: ?ThreadInfo,
+  +communityThreadInfo: ?ThreadInfo,
+  +containingThreadInfo: ?ThreadInfo,
 }) {
   const { id } = userInfo;
   if (excludeUserIDs.includes(id) || id in results) {
@@ -99,8 +98,8 @@
   +userInfos: { +[id: string]: AccountUserInfo },
   +excludeUserIDs: $ReadOnlyArray<string>,
   +includeServerSearchUsers?: $ReadOnlyArray<GlobalAccountUserInfo>,
-  +inputParentThreadInfo?: ?LegacyThreadInfo | ?ThreadInfo,
-  +inputCommunityThreadInfo?: ?LegacyThreadInfo | ?ThreadInfo,
+  +inputParentThreadInfo?: ?ThreadInfo,
+  +inputCommunityThreadInfo?: ?ThreadInfo,
   +threadType?: ?ThreadType,
 }): UserListItem[] {
   const memoizedUserInfos = React.useMemo(() => values(userInfos), [userInfos]);
diff --git a/lib/shared/user-utils.js b/lib/shared/user-utils.js
--- a/lib/shared/user-utils.js
+++ b/lib/shared/user-utils.js
@@ -6,10 +6,7 @@
   ThreadInfo,
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
-import type {
-  LegacyThreadInfo,
-  ServerThreadInfo,
-} from '../types/thread-types.js';
+import type { ServerThreadInfo } from '../types/thread-types.js';
 import type { UserInfo } from '../types/user-types.js';
 import { useSelector } from '../utils/redux-utils.js';
 
@@ -36,7 +33,7 @@
 }
 
 function useKeyserverAdmin(
-  community: LegacyThreadInfo | ThreadInfo | RawThreadInfo | ServerThreadInfo,
+  community: ThreadInfo | RawThreadInfo | ServerThreadInfo,
 ): ?UserInfo {
   const userInfos = useSelector(state => state.userStore.userInfos);
   // This hack only works as long as there is only one admin
diff --git a/lib/utils/drawer-utils.react.js b/lib/utils/drawer-utils.react.js
--- a/lib/utils/drawer-utils.react.js
+++ b/lib/utils/drawer-utils.react.js
@@ -10,7 +10,6 @@
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import { communitySubthreads } from '../types/thread-types-enum.js';
-import type { LegacyThreadInfo } from '../types/thread-types.js';
 
 type WritableCommunityDrawerItemData<T> = {
   threadInfo: ThreadInfo,
@@ -105,7 +104,7 @@
 function filterThreadIDsBelongingToCommunity(
   communityID: string,
   threadInfosObj: {
-    +[id: string]: RawThreadInfo | LegacyThreadInfo | ThreadInfo,
+    +[id: string]: RawThreadInfo | ThreadInfo,
   },
 ): $ReadOnlySet<string> {
   const threadInfos = values(threadInfosObj);
diff --git a/lib/utils/message-pinning-utils.js b/lib/utils/message-pinning-utils.js
--- a/lib/utils/message-pinning-utils.js
+++ b/lib/utils/message-pinning-utils.js
@@ -8,18 +8,11 @@
   RawThreadInfo,
 } from '../types/minimally-encoded-thread-permissions-types.js';
 import { threadPermissions } from '../types/thread-permission-types.js';
-import type {
-  LegacyRawThreadInfo,
-  LegacyThreadInfo,
-} from '../types/thread-types.js';
+import type { LegacyRawThreadInfo } from '../types/thread-types.js';
 
 function canToggleMessagePin(
   messageInfo: RawMessageInfo | MessageInfo,
-  threadInfo:
-    | LegacyRawThreadInfo
-    | RawThreadInfo
-    | LegacyThreadInfo
-    | ThreadInfo,
+  threadInfo: LegacyRawThreadInfo | RawThreadInfo | ThreadInfo,
 ): boolean {
   const isValidMessage = !isInvalidPinSourceForThread(messageInfo, threadInfo);
   const hasManagePinsPermission = threadHasPermission(
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
@@ -10,11 +10,7 @@
   type ThreadRolePermissionsBlob,
   type UserSurfacedPermission,
 } from '../types/thread-permission-types.js';
-import type {
-  LegacyThreadInfo,
-  RelativeMemberInfo,
-  RoleInfo,
-} from '../types/thread-types';
+import type { RelativeMemberInfo, RoleInfo } from '../types/thread-types';
 import { threadTypes } from '../types/thread-types-enum.js';
 
 function constructRoleDeletionMessagePrompt(
@@ -57,7 +53,7 @@
 }
 
 function useRolesFromCommunityThreadInfo(
-  threadInfo: LegacyThreadInfo | ThreadInfo,
+  threadInfo: ThreadInfo,
   memberInfos: $ReadOnlyArray<RelativeMemberInfo>,
 ): $ReadOnlyMap<string, ?RoleInfo> {
   // Our in-code system has chat-specific roles, while the