diff --git a/lib/types/account-types.js b/lib/types/account-types.js
--- a/lib/types/account-types.js
+++ b/lib/types/account-types.js
@@ -15,7 +15,7 @@
   type GenericMessagesResult,
 } from './message-types.js';
 import type { PreRequestUserState } from './session-types.js';
-import { type LegacyRawThreadInfos } from './thread-types.js';
+import { type RawThreadInfos } from './thread-types.js';
 import {
   type UserInfo,
   type LoggedOutUserInfo,
@@ -69,7 +69,7 @@
   rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   currentUserInfo: LoggedInUserInfo,
   cookieChange: {
-    threadInfos: LegacyRawThreadInfos,
+    threadInfos: RawThreadInfos,
     userInfos: $ReadOnlyArray<UserInfo>,
   },
 };
@@ -77,7 +77,7 @@
 export type RegisterResult = {
   +currentUserInfo: LoggedInUserInfo,
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
-  +threadInfos: LegacyRawThreadInfos,
+  +threadInfos: RawThreadInfos,
   +userInfos: $ReadOnlyArray<UserInfo>,
   +calendarQuery: CalendarQuery,
 };
@@ -142,14 +142,14 @@
   +rawEntryInfos?: ?$ReadOnlyArray<RawEntryInfo>,
   +serverTime: number,
   +cookieChange: {
-    +threadInfos: LegacyRawThreadInfos,
+    +threadInfos: RawThreadInfos,
     +userInfos: $ReadOnlyArray<UserInfo>,
   },
   +notAcknowledgedPolicies?: $ReadOnlyArray<PolicyType>,
 };
 
 export type LogInResult = {
-  +threadInfos: LegacyRawThreadInfos,
+  +threadInfos: RawThreadInfos,
   +currentUserInfo: LoggedInUserInfo,
   +messagesResult: GenericMessagesResult,
   +userInfos: $ReadOnlyArray<UserInfo>,
diff --git a/lib/types/request-types.js b/lib/types/request-types.js
--- a/lib/types/request-types.js
+++ b/lib/types/request-types.js
@@ -19,8 +19,8 @@
   ClientEntryInconsistencyReportShape,
 } from './report-types.js';
 import {
-  type LegacyRawThreadInfo,
   legacyRawThreadInfoValidator,
+  type RawThreadInfo,
 } from './thread-types.js';
 import {
   type CurrentUserInfo,
@@ -105,7 +105,7 @@
 }>;
 
 type StateChanges = Partial<{
-  +rawThreadInfos: LegacyRawThreadInfo[],
+  +rawThreadInfos: RawThreadInfo[],
   +rawEntryInfos: RawEntryInfo[],
   +currentUserInfo: CurrentUserInfo,
   +userInfos: AccountUserInfo[],
@@ -230,7 +230,7 @@
     +userInfos: boolean,
   }>,
   +stateChanges?: Partial<{
-    +rawThreadInfos: LegacyRawThreadInfo[],
+    +rawThreadInfos: RawThreadInfo[],
     +rawEntryInfos: RawEntryInfo[],
     +currentUserInfo: CurrentUserInfo,
     +userInfos: AccountUserInfo[],
diff --git a/lib/types/session-types.js b/lib/types/session-types.js
--- a/lib/types/session-types.js
+++ b/lib/types/session-types.js
@@ -4,7 +4,7 @@
 
 import type { LogInActionSource } from './account-types.js';
 import type { CalendarQuery } from './entry-types.js';
-import type { LegacyRawThreadInfos } from './thread-types.js';
+import type { RawThreadInfos } from './thread-types.js';
 import {
   type UserInfo,
   type CurrentUserInfo,
@@ -37,14 +37,14 @@
 export type ServerSessionChange =
   | {
       cookieInvalidated: false,
-      threadInfos: LegacyRawThreadInfos,
+      threadInfos: RawThreadInfos,
       userInfos: $ReadOnlyArray<UserInfo>,
       sessionID?: null | string,
       cookie?: string,
     }
   | {
       cookieInvalidated: true,
-      threadInfos: LegacyRawThreadInfos,
+      threadInfos: RawThreadInfos,
       userInfos: $ReadOnlyArray<UserInfo>,
       currentUserInfo: LoggedOutUserInfo,
       sessionID?: null | string,
diff --git a/lib/types/socket-types.js b/lib/types/socket-types.js
--- a/lib/types/socket-types.js
+++ b/lib/types/socket-types.js
@@ -34,8 +34,8 @@
 } from './request-types.js';
 import type { SessionState, SessionIdentification } from './session-types.js';
 import {
+  type RawThreadInfos,
   legacyRawThreadInfoValidator,
-  type LegacyRawThreadInfos,
 } from './thread-types.js';
 import {
   type ClientUpdatesResult,
@@ -186,7 +186,7 @@
 export const fullStateSyncActionType = 'FULL_STATE_SYNC';
 export type BaseFullStateSync = {
   +messagesResult: MessagesResponse,
-  +threadInfos: LegacyRawThreadInfos,
+  +threadInfos: RawThreadInfos,
   +rawEntryInfos: $ReadOnlyArray<RawEntryInfo>,
   +userInfos: $ReadOnlyArray<UserInfo>,
   +updatesCurrentAsOf: number,
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
@@ -148,6 +148,9 @@
 export type RawThreadInfos = {
   +[id: string]: RawThreadInfo,
 };
+export type MinimallyEncodedRawThreadInfos = {
+  +[id: string]: MinimallyEncodedRawThreadInfo,
+};
 
 export type LegacyThreadInfo = {
   +id: string,
@@ -244,7 +247,7 @@
 };
 
 export type ThreadStore = {
-  +threadInfos: LegacyRawThreadInfos,
+  +threadInfos: RawThreadInfos,
 };
 export const threadStoreValidator: TInterface<ThreadStore> =
   tShape<ThreadStore>({
diff --git a/lib/types/update-types.js b/lib/types/update-types.js
--- a/lib/types/update-types.js
+++ b/lib/types/update-types.js
@@ -7,7 +7,7 @@
   type RawMessageInfo,
   type MessageTruncationStatus,
 } from './message-types.js';
-import { type LegacyRawThreadInfo } from './thread-types.js';
+import type { RawThreadInfo } from './thread-types.js';
 import {
   type UserInfo,
   userInfoValidator,
@@ -183,7 +183,7 @@
   +type: 1,
   +id: string,
   +time: number,
-  +threadInfo: LegacyRawThreadInfo,
+  +threadInfo: RawThreadInfo,
 };
 
 export type ThreadReadStatusUpdateInfo = {
@@ -205,7 +205,7 @@
   +type: 4,
   +id: string,
   +time: number,
-  +threadInfo: LegacyRawThreadInfo,
+  +threadInfo: RawThreadInfo,
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +truncationStatus: MessageTruncationStatus,
   +rawEntryInfos: $ReadOnlyArray<RawEntryInfo>,