diff --git a/lib/shared/dm-ops/add-viewer-to-thread-members-spec.js b/lib/shared/dm-ops/add-viewer-to-thread-members-spec.js
--- a/lib/shared/dm-ops/add-viewer-to-thread-members-spec.js
+++ b/lib/shared/dm-ops/add-viewer-to-thread-members-spec.js
@@ -8,6 +8,7 @@
 import type { DMAddViewerToThreadMembersOperation } from '../../types/dm-ops.js';
 import { messageTypes } from '../../types/message-types-enum.js';
 import { messageTruncationStatus } from '../../types/message-types.js';
+import { joinThreadSubscription } from '../../types/subscription-types.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 
 function createAddViewerToThreadMembersResults(
@@ -28,7 +29,13 @@
   const resultThreadInfo = createThickRawThreadInfo(
     {
       ...existingThreadDetails,
-      allMemberIDs: [...existingThreadDetails.allMemberIDs, ...addedUserIDs],
+      allMemberIDWithSubscriptions: [
+        ...existingThreadDetails.allMemberIDWithSubscriptions,
+        ...addedUserIDs.map(id => ({
+          id,
+          subscription: joinThreadSubscription,
+        })),
+      ],
     },
     viewerID,
   );
diff --git a/lib/shared/dm-ops/change-thread-subscription.js b/lib/shared/dm-ops/change-thread-subscription.js
new file mode 100644
--- /dev/null
+++ b/lib/shared/dm-ops/change-thread-subscription.js
@@ -0,0 +1,79 @@
+// @flow
+
+import invariant from 'invariant';
+import uuid from 'uuid';
+
+import type {
+  ProcessDMOperationUtilities,
+  DMOperationSpec,
+} from './dm-op-spec.js';
+import type { DMChangeThreadSubscriptionOperation } from '../../types/dm-ops.js';
+import { updateTypes } from '../../types/update-types-enum.js';
+import type { ClientUpdateInfo } from '../../types/update-types.js';
+
+const changeThreadSubscriptionSpec: DMOperationSpec<DMChangeThreadSubscriptionOperation> =
+  Object.freeze({
+    processDMOperation: async (
+      dmOperation: DMChangeThreadSubscriptionOperation,
+      viewerID: string,
+      utilities: ProcessDMOperationUtilities,
+    ) => {
+      const { creatorID, threadID, subscription, time } = dmOperation;
+
+      const threadInfo = utilities.threadInfos[threadID];
+      invariant(threadInfo.thick, 'Thread should be thick');
+
+      const creatorMemberInfo = threadInfo.members.find(
+        member => member.id === creatorID,
+      );
+      invariant(creatorMemberInfo, 'operation creator missing in thread');
+      const updatedCreatorMemberInfo = {
+        ...creatorMemberInfo,
+        subscription,
+      };
+      const otherMemberInfos = threadInfo.members.filter(
+        member => member.id !== creatorID,
+      );
+      const membersUpdate = [...otherMemberInfos, updatedCreatorMemberInfo];
+
+      const threadInfoUpdate = {
+        ...threadInfo,
+        members: membersUpdate,
+      };
+      const updateInfos: Array<ClientUpdateInfo> = [
+        {
+          type: updateTypes.UPDATE_THREAD,
+          id: uuid.v4(),
+          time,
+          threadInfo: threadInfoUpdate,
+        },
+      ];
+
+      return { updateInfos, rawMessageInfos: [] };
+    },
+    canBeProcessed(
+      dmOperation: DMChangeThreadSubscriptionOperation,
+      viewerID: string,
+      utilities: ProcessDMOperationUtilities,
+    ) {
+      const { threadID, creatorID } = dmOperation;
+      if (!utilities.threadInfos[threadID]) {
+        return {
+          isProcessingPossible: false,
+          reason: { type: 'missing_thread', threadID },
+        };
+      }
+
+      if (
+        !utilities.threadInfos[threadID].members.find(
+          memberInfo => memberInfo.id === creatorID,
+        )
+      ) {
+        return { isProcessingPossible: false, reason: { type: 'invalid' } };
+      }
+
+      return { isProcessingPossible: true };
+    },
+  });
+
+export { changeThreadSubscriptionSpec };
diff --git a/lib/shared/dm-ops/create-sidebar-spec.js b/lib/shared/dm-ops/create-sidebar-spec.js
--- a/lib/shared/dm-ops/create-sidebar-spec.js
+++ b/lib/shared/dm-ops/create-sidebar-spec.js
@@ -13,6 +13,7 @@
   type RawMessageInfo,
   messageTruncationStatus,
 } from '../../types/message-types.js';
+import { joinThreadSubscription } from '../../types/subscription-types.js';
 import { threadTypes } from '../../types/thread-types-enum.js';
 import { updateTypes } from '../../types/update-types-enum.js';
 import { isInvalidSidebarSource } from '../message-utils.js';
@@ -36,6 +37,10 @@
         newCreateSidebarMessageID,
       } = dmOperation;
       const allMemberIDs = [creatorID, ...memberIDs];
+      const allMemberIDWithSubscriptions = allMemberIDs.map(id => ({
+        id,
+        subscription: joinThreadSubscription,
+      }));
 
       const rawThreadInfo = createThickRawThreadInfo(
         {
@@ -43,7 +48,7 @@
           threadType: threadTypes.THICK_SIDEBAR,
           creationTime: time,
           parentThreadID,
-          allMemberIDs,
+          allMemberIDWithSubscriptions,
           roleID,
           creatorID,
           sourceMessageID,
diff --git a/lib/shared/dm-ops/create-thread-spec.js b/lib/shared/dm-ops/create-thread-spec.js
--- a/lib/shared/dm-ops/create-thread-spec.js
+++ b/lib/shared/dm-ops/create-thread-spec.js
@@ -67,7 +67,7 @@
     threadType,
     creationTime,
     parentThreadID,
-    allMemberIDs,
+    allMemberIDWithSubscriptions,
     roleID,
     creatorID,
     name,
@@ -80,7 +80,11 @@
     pinnedCount,
   } = input;
 
-  const threadColor = color ?? generatePendingThreadColor(allMemberIDs);
+  const threadColor =
+    color ??
+    generatePendingThreadColor(
+      allMemberIDWithSubscriptions.map(({ id }) => id),
+    );
 
   const { membershipPermissions, role } =
     createRoleAndPermissionForThickThreads(threadType, threadID, roleID);
@@ -93,14 +97,15 @@
     color: threadColor,
     creationTime,
     parentThreadID,
-    members: allMemberIDs.map(memberID =>
-      minimallyEncodeMemberInfo<ThickMemberInfo>({
-        id: memberID,
-        role: role.id,
-        permissions: membershipPermissions,
-        isSender: memberID === viewerID,
-        subscription: joinThreadSubscription,
-      }),
+    members: allMemberIDWithSubscriptions.map(
+      ({ id: memberID, subscription }) =>
+        minimallyEncodeMemberInfo<ThickMemberInfo>({
+          id: memberID,
+          role: role.id,
+          permissions: membershipPermissions,
+          isSender: memberID === viewerID,
+          subscription: subscription,
+        }),
     ),
     roles: {
       [role.id]: role,
@@ -142,13 +147,17 @@
         newMessageID,
       } = dmOperation;
       const allMemberIDs = [creatorID, ...memberIDs];
+      const allMemberIDWithSubscriptions = allMemberIDs.map(id => ({
+        id,
+        subscription: joinThreadSubscription,
+      }));
 
       const rawThreadInfo = createThickRawThreadInfo(
         {
           threadID,
           threadType,
           creationTime: time,
-          allMemberIDs,
+          allMemberIDWithSubscriptions,
           roleID,
           creatorID,
         },
diff --git a/lib/shared/dm-ops/dm-op-specs.js b/lib/shared/dm-ops/dm-op-specs.js
--- a/lib/shared/dm-ops/dm-op-specs.js
+++ b/lib/shared/dm-ops/dm-op-specs.js
@@ -4,6 +4,7 @@
 import { addViewerToThreadMembersSpec } from './add-viewer-to-thread-members-spec.js';
 import { changeThreadSettingsAndAddViewerSpec } from './change-thread-settings-and-add-viewer-spec.js';
 import { changeThreadSettingsSpec } from './change-thread-settings-spec.js';
+import { changeThreadSubscriptionSpec } from './change-thread-subscription.js';
 import { createSidebarSpec } from './create-sidebar-spec.js';
 import { createThreadSpec } from './create-thread-spec.js';
 import type { DMOperationSpec } from './dm-op-spec.js';
@@ -31,4 +32,5 @@
   [dmOperationTypes.CHANGE_THREAD_SETTINGS]: changeThreadSettingsSpec,
   [dmOperationTypes.CHANGE_THREAD_SETTINGS_AND_ADD_VIEWER]:
     changeThreadSettingsAndAddViewerSpec,
+  [dmOperationTypes.CHANGE_THREAD_SUBSCRIPTION]: changeThreadSubscriptionSpec,
 });
diff --git a/lib/shared/dm-ops/join-thread-spec.js b/lib/shared/dm-ops/join-thread-spec.js
--- a/lib/shared/dm-ops/join-thread-spec.js
+++ b/lib/shared/dm-ops/join-thread-spec.js
@@ -57,7 +57,10 @@
       const newThreadInfo = createThickRawThreadInfo(
         {
           ...existingThreadDetails,
-          allMemberIDs: [...existingThreadDetails.allMemberIDs, joinerID],
+          allMemberIDWithSubscriptions: [
+            ...existingThreadDetails.allMemberIDWithSubscriptions,
+            { id: joinerID, subscription: joinThreadSubscription },
+          ],
         },
         viewerID,
       );
diff --git a/lib/types/dm-ops.js b/lib/types/dm-ops.js
--- a/lib/types/dm-ops.js
+++ b/lib/types/dm-ops.js
@@ -5,6 +5,10 @@
 import { clientAvatarValidator, type ClientAvatar } from './avatar-types.js';
 import type { RawMessageInfo } from './message-types.js';
 import type { OutboundP2PMessage } from './sqlite-types.js';
+import {
+  type ThreadSubscription,
+  threadSubscriptionValidator,
+} from './subscription-types.js';
 import {
   type NonSidebarThickThreadType,
   nonSidebarThickThreadTypes,
@@ -29,15 +33,26 @@
   CHANGE_THREAD_SETTINGS: 'change_thread_settings',
   CHANGE_THREAD_SETTINGS_AND_ADD_VIEWER:
     'change_thread_settings_and_add_viewer',
+  CHANGE_THREAD_SUBSCRIPTION: 'change_thread_subscription',
 });
 export type DMOperationType = $Values<typeof dmOperationTypes>;
 
+type MemberIDWithSubscription = {
+  +id: string,
+  +subscription: ThreadSubscription,
+};
+export const memberIDWithSubscriptionValidator: TInterface<MemberIDWithSubscription> =
+  tShape<MemberIDWithSubscription>({
+    id: tUserID,
+    subscription: threadSubscriptionValidator,
+  });
+
 export type CreateThickRawThreadInfoInput = {
   +threadID: string,
   +threadType: ThickThreadType,
   +creationTime: number,
   +parentThreadID?: ?string,
-  +allMemberIDs: $ReadOnlyArray<string>,
+  +allMemberIDWithSubscriptions: $ReadOnlyArray<MemberIDWithSubscription>,
   +roleID: string,
   +creatorID: string,
   +name?: ?string,
@@ -55,7 +70,7 @@
     threadType: thickThreadTypeValidator,
     creationTime: t.Number,
     parentThreadID: t.maybe(t.String),
-    allMemberIDs: t.list(tUserID),
+    allMemberIDWithSubscriptions: t.list(memberIDWithSubscriptionValidator),
     roleID: t.String,
     creatorID: tUserID,
     name: t.maybe(t.String),
@@ -313,6 +328,22 @@
     ...dmChangeThreadSettingsBaseValidatorShape,
   });
 
+export type DMChangeThreadSubscriptionOperation = {
+  +type: 'change_thread_subscription',
+  +time: number,
+  +threadID: string,
+  +creatorID: string,
+  +subscription: ThreadSubscription,
+};
+export const dmChangeThreadSubscriptionOperationValidator: TInterface<DMChangeThreadSubscriptionOperation> =
+  tShape<DMChangeThreadSubscriptionOperation>({
+    type: tString(dmOperationTypes.CHANGE_THREAD_SUBSCRIPTION),
+    time: t.Number,
+    threadID: t.String,
+    creatorID: tUserID,
+    subscription: threadSubscriptionValidator,
+  });
+
 export type DMOperation =
   | DMCreateThreadOperation
   | DMCreateSidebarOperation
@@ -325,7 +356,8 @@
   | DMLeaveThreadOperation
   | DMRemoveMembersOperation
   | DMChangeThreadSettingsOperation
-  | DMChangeThreadSettingsAndAddViewerOperation;
+  | DMChangeThreadSettingsAndAddViewerOperation
+  | DMChangeThreadSubscriptionOperation;
 export const dmOperationValidator: TUnion<DMOperation> = t.union([
   dmCreateThreadOperationValidator,
   dmCreateSidebarOperationValidator,
@@ -339,6 +371,7 @@
   dmRemoveMembersOperationValidator,
   dmChangeThreadSettingsOperationValidator,
   dmChangeThreadSettingsAndAddViewerOperationValidator,
+  dmChangeThreadSubscriptionOperationValidator,
 ]);
 
 export type DMOperationResult = {