diff --git a/packages/framework/presence/api-report/presence.alpha.api.md b/packages/framework/presence/api-report/presence.alpha.api.md
index 116ba0484450..0b74359f11c6 100644
--- a/packages/framework/presence/api-report/presence.alpha.api.md
+++ b/packages/framework/presence/api-report/presence.alpha.api.md
@@ -112,12 +112,12 @@ export namespace InternalTypes {
     // @system (undocumented)
     export interface ValueOptionalState<TValue> extends ValueStateMetadata {
         // (undocumented)
-        value?: JsonDeserialized<TValue>;
+        value?: OpaqueJsonDeserialized<TValue>;
     }
     // @system (undocumented)
     export interface ValueRequiredState<TValue> extends ValueStateMetadata {
         // (undocumented)
-        value: JsonDeserialized<TValue>;
+        value: OpaqueJsonDeserialized<TValue>;
     }
     // @system (undocumented)
     export interface ValueStateMetadata {
@@ -128,18 +128,20 @@ export namespace InternalTypes {
     }
 }
 
-// @alpha @system
+// @beta @system
 export namespace InternalUtilityTypes {
     // @system
-    export type IsNotificationListener<Event> = Event extends (...args: infer P) => void ? InternalUtilityTypes_2.IfSameType<P, JsonSerializable<P> & JsonDeserialized<P>, true, false> : false;
+    export type IsNotificationListener<Event> = Event extends (...args: infer P) => void ? InternalUtilityTypes_2.IfSameType<P, JsonSerializable_2<P> & JsonDeserialized_2<P>, true, false> : false;
     // @system
-    export type JsonDeserializedParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonDeserialized<P> : never;
+    export type JsonDeserializedParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonDeserialized_2<P> : never;
     // @system
-    export type JsonSerializableParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonSerializable<P> : never;
+    export type JsonSerializableParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonSerializable_2<P> : never;
     // @system
     export type NotificationListeners<E> = {
         [P in string & keyof E as IsNotificationListener<E[P]> extends true ? P : never]: E[P];
     };
+    // @system (undocumented)
+    export type OpaqueJsonSerializable<T> = JsonSerializableBrand<T>;
 }
 
 // @beta
@@ -147,7 +149,7 @@ export function latest<T extends object | null, Key extends string = string>(arg
 
 // @beta
 export interface LatestArguments<T extends object | null> {
-    local: JsonSerializable<T> & JsonDeserialized<T> & (object | null);
+    local: JsonSerializable_2<T> & JsonDeserialized_2<T> & (object | null);
     settings?: BroadcastControlSettings | undefined;
 }
 
@@ -162,7 +164,7 @@ export interface LatestData<T> {
     // (undocumented)
     metadata: LatestMetadata;
     // (undocumented)
-    value: DeepReadonly<JsonDeserialized<T>>;
+    value: DeepReadonly<JsonDeserialized_2<T>>;
 }
 
 // @beta
@@ -171,7 +173,7 @@ export function latestMap<T, Keys extends string | number = string | number, Reg
 // @beta
 export interface LatestMapArguments<T, Keys extends string | number = string | number> {
     local?: {
-        [K in Keys]: JsonSerializable<T> & JsonDeserialized<T>;
+        [K in Keys]: JsonSerializable_2<T> & JsonDeserialized_2<T>;
     };
     settings?: BroadcastControlSettings | undefined;
 }
@@ -218,7 +220,7 @@ export interface LatestMapRawEvents<T, K extends string | number> {
     }) => void;
     // @eventProperty
     localItemUpdated: (updatedItem: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly<JsonSerializable_2<T> & JsonDeserialized_2<T>>;
         key: K;
     }) => void;
     // @eventProperty
@@ -242,8 +244,8 @@ export interface LatestRaw<T> {
     getRemote(attendee: Attendee): LatestData<T>;
     getRemotes(): IterableIterator<LatestClientData<T>>;
     getStateAttendees(): Attendee[];
-    get local(): DeepReadonly<JsonDeserialized<T>>;
-    set local(value: JsonSerializable<T> & JsonDeserialized<T>);
+    get local(): DeepReadonly<JsonDeserialized_2<T>>;
+    set local(value: JsonSerializable_2<T> & JsonDeserialized_2<T>);
     readonly presence: Presence;
 }
 
@@ -251,7 +253,7 @@ export interface LatestRaw<T> {
 export interface LatestRawEvents<T> {
     // @eventProperty
     localUpdated: (update: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly<JsonSerializable_2<T> & JsonDeserialized_2<T>>;
     }) => void;
     // @eventProperty
     remoteUpdated: (update: LatestClientData<T>) => void;
@@ -344,12 +346,12 @@ export interface StateMap<K extends string | number, V> {
     clear(): void;
     // (undocumented)
     delete(key: K): boolean;
-    forEach(callbackfn: (value: DeepReadonly<JsonDeserialized<V>>, key: K, map: StateMap<K, V>) => void, thisArg?: unknown): void;
-    get(key: K): DeepReadonly<JsonDeserialized<V>> | undefined;
+    forEach(callbackfn: (value: DeepReadonly<JsonDeserialized_2<V>>, key: K, map: StateMap<K, V>) => void, thisArg?: unknown): void;
+    get(key: K): DeepReadonly<JsonDeserialized_2<V>> | undefined;
     // (undocumented)
     has(key: K): boolean;
     keys(): IterableIterator<K>;
-    set(key: K, value: JsonSerializable<V> & JsonDeserialized<V>): this;
+    set(key: K, value: JsonSerializable_2<V> & JsonDeserialized_2<V>): this;
     // (undocumented)
     readonly size: number;
 }
diff --git a/packages/framework/presence/api-report/presence.beta.api.md b/packages/framework/presence/api-report/presence.beta.api.md
index c68db527364d..6b42795f3970 100644
--- a/packages/framework/presence/api-report/presence.beta.api.md
+++ b/packages/framework/presence/api-report/presence.beta.api.md
@@ -99,12 +99,12 @@ export namespace InternalTypes {
     // @system (undocumented)
     export interface ValueOptionalState<TValue> extends ValueStateMetadata {
         // (undocumented)
-        value?: JsonDeserialized<TValue>;
+        value?: OpaqueJsonDeserialized<TValue>;
     }
     // @system (undocumented)
     export interface ValueRequiredState<TValue> extends ValueStateMetadata {
         // (undocumented)
-        value: JsonDeserialized<TValue>;
+        value: OpaqueJsonDeserialized<TValue>;
     }
     // @system (undocumented)
     export interface ValueStateMetadata {
@@ -115,12 +115,28 @@ export namespace InternalTypes {
     }
 }
 
+// @beta @system
+export namespace InternalUtilityTypes {
+    // @system
+    export type IsNotificationListener<Event> = Event extends (...args: infer P) => void ? InternalUtilityTypes_2.IfSameType<P, JsonSerializable_2<P> & JsonDeserialized_2<P>, true, false> : false;
+    // @system
+    export type JsonDeserializedParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonDeserialized_2<P> : never;
+    // @system
+    export type JsonSerializableParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonSerializable_2<P> : never;
+    // @system
+    export type NotificationListeners<E> = {
+        [P in string & keyof E as IsNotificationListener<E[P]> extends true ? P : never]: E[P];
+    };
+    // @system (undocumented)
+    export type OpaqueJsonSerializable<T> = JsonSerializableBrand<T>;
+}
+
 // @beta
 export function latest<T extends object | null, Key extends string = string>(args: LatestArguments<T>): InternalTypes.ManagerFactory<Key, InternalTypes.ValueRequiredState<T>, LatestRaw<T>>;
 
 // @beta
 export interface LatestArguments<T extends object | null> {
-    local: JsonSerializable<T> & JsonDeserialized<T> & (object | null);
+    local: JsonSerializable_2<T> & JsonDeserialized_2<T> & (object | null);
     settings?: BroadcastControlSettings | undefined;
 }
 
@@ -135,7 +151,7 @@ export interface LatestData<T> {
     // (undocumented)
     metadata: LatestMetadata;
     // (undocumented)
-    value: DeepReadonly<JsonDeserialized<T>>;
+    value: DeepReadonly<JsonDeserialized_2<T>>;
 }
 
 // @beta
@@ -144,7 +160,7 @@ export function latestMap<T, Keys extends string | number = string | number, Reg
 // @beta
 export interface LatestMapArguments<T, Keys extends string | number = string | number> {
     local?: {
-        [K in Keys]: JsonSerializable<T> & JsonDeserialized<T>;
+        [K in Keys]: JsonSerializable_2<T> & JsonDeserialized_2<T>;
     };
     settings?: BroadcastControlSettings | undefined;
 }
@@ -191,7 +207,7 @@ export interface LatestMapRawEvents<T, K extends string | number> {
     }) => void;
     // @eventProperty
     localItemUpdated: (updatedItem: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly<JsonSerializable_2<T> & JsonDeserialized_2<T>>;
         key: K;
     }) => void;
     // @eventProperty
@@ -215,8 +231,8 @@ export interface LatestRaw<T> {
     getRemote(attendee: Attendee): LatestData<T>;
     getRemotes(): IterableIterator<LatestClientData<T>>;
     getStateAttendees(): Attendee[];
-    get local(): DeepReadonly<JsonDeserialized<T>>;
-    set local(value: JsonSerializable<T> & JsonDeserialized<T>);
+    get local(): DeepReadonly<JsonDeserialized_2<T>>;
+    set local(value: JsonSerializable_2<T> & JsonDeserialized_2<T>);
     readonly presence: Presence;
 }
 
@@ -224,7 +240,7 @@ export interface LatestRaw<T> {
 export interface LatestRawEvents<T> {
     // @eventProperty
     localUpdated: (update: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly<JsonSerializable_2<T> & JsonDeserialized_2<T>>;
     }) => void;
     // @eventProperty
     remoteUpdated: (update: LatestClientData<T>) => void;
@@ -262,12 +278,12 @@ export interface StateMap<K extends string | number, V> {
     clear(): void;
     // (undocumented)
     delete(key: K): boolean;
-    forEach(callbackfn: (value: DeepReadonly<JsonDeserialized<V>>, key: K, map: StateMap<K, V>) => void, thisArg?: unknown): void;
-    get(key: K): DeepReadonly<JsonDeserialized<V>> | undefined;
+    forEach(callbackfn: (value: DeepReadonly<JsonDeserialized_2<V>>, key: K, map: StateMap<K, V>) => void, thisArg?: unknown): void;
+    get(key: K): DeepReadonly<JsonDeserialized_2<V>> | undefined;
     // (undocumented)
     has(key: K): boolean;
     keys(): IterableIterator<K>;
-    set(key: K, value: JsonSerializable<V> & JsonDeserialized<V>): this;
+    set(key: K, value: JsonSerializable_2<V> & JsonDeserialized_2<V>): this;
     // (undocumented)
     readonly size: number;
 }
diff --git a/packages/framework/presence/src/exposedInternalTypes.ts b/packages/framework/presence/src/exposedInternalTypes.ts
index 46e457098129..a08ced3c0065 100644
--- a/packages/framework/presence/src/exposedInternalTypes.ts
+++ b/packages/framework/presence/src/exposedInternalTypes.ts
@@ -3,10 +3,11 @@
  * Licensed under the MIT License.
  */
 
+import type { OpaqueJsonDeserialized } from "@fluidframework/container-runtime-definitions/internal";
 import type {
 	JsonDeserialized,
 	JsonSerializable,
-} from "@fluidframework/core-interfaces/internal/exposedUtilityTypes";
+} from "@fluidframework/core-interfaces/internal";
 
 /**
  * Collection of value types that are not intended to be used/imported
@@ -29,14 +30,14 @@ export namespace InternalTypes {
 	 * @system
 	 */
 	export interface ValueOptionalState<TValue> extends ValueStateMetadata {
-		value?: JsonDeserialized<TValue>;
+		value?: OpaqueJsonDeserialized<TValue>;
 	}
 
 	/**
 	 * @system
 	 */
 	export interface ValueRequiredState<TValue> extends ValueStateMetadata {
-		value: JsonDeserialized<TValue>;
+		value: OpaqueJsonDeserialized<TValue>;
 	}
 
 	/**
diff --git a/packages/framework/presence/src/exposedUtilityTypes.ts b/packages/framework/presence/src/exposedUtilityTypes.ts
index a6df51d9f084..5d6595ad699b 100644
--- a/packages/framework/presence/src/exposedUtilityTypes.ts
+++ b/packages/framework/presence/src/exposedUtilityTypes.ts
@@ -3,17 +3,22 @@
  * Licensed under the MIT License.
  */
 
+import { BrandedType } from "@fluidframework/core-interfaces/internal";
 import type {
+	DeepReadonly,
 	InternalUtilityTypes as CoreInternalUtilityTypes,
 	JsonDeserialized,
 	JsonSerializable,
 } from "@fluidframework/core-interfaces/internal/exposedUtilityTypes";
 
+import { asDeeplyReadonly } from "./internalUtils.js";
+import type { OpaqueJsonDeserialized } from "@fluidframework/container-runtime-definitions/internal";
+
 /**
  * Collection of utility types that are not intended to be used/imported
  * directly outside of this package.
  *
- * @alpha
+ * @beta
  * @system
  */
 // eslint-disable-next-line @typescript-eslint/no-namespace
@@ -76,4 +81,63 @@ export namespace InternalUtilityTypes {
 	) => any
 		? JsonSerializable<P>
 		: never;
+
+	/**
+	 * @internal
+	 * @system
+	 */
+	declare class JsonDeserializedBrand<T> extends BrandedType<T> {
+		private readonly EncodedValue: T;
+		private constructor();
+	}
+
+	/**
+	 * @system
+	 */
+	// export type JsonDeserializedHandle<T> = Tagged<JsonDeserialized<T>, "JsonDeserialized">;
+	// export type OpaqueJsonDeserialized<T> = UnverifiedBrand<T>;
+	// export type OpaqueJsonDeserialized<T> = JsonDeserializedBrand<T>;
+	// export type OpaqueJsonDeserialized<T extends JsonDeserialized<U>, U> = JsonDeserializedBrand<T, U>;
+
+	/**
+	 * @internal
+	 * @system
+	 */
+	export declare class JsonSerializableBrand<T> extends BrandedType<T> {
+		private readonly JsonSerializable: JsonSerializable<T>;
+		private constructor();
+	}
+
+	/**
+	 * @system
+	 */
+	// export type JsonDeserializedHandle<T> = Tagged<JsonDeserialized<T>, "JsonDeserialized">;
+	export type OpaqueJsonSerializable<T> = JsonSerializableBrand<T>;
+}
+
+/**
+ * Cast a JsonDeserialized value to its branded version.
+ *
+ * @system
+ */
+export function brandJson<T>(value: JsonDeserialized<T>): OpaqueJsonDeserialized<T> {
+	return value as OpaqueJsonDeserialized<T>;
+}
+
+/**
+ * Cast a branded JsonDeserialized value back to its unbranded version.
+ *
+ * @system
+ */
+export function unbrandJson<T>(value: OpaqueJsonDeserialized<T>): JsonDeserialized<T> {
+	return value as JsonDeserialized<T>;
+}
+
+/**
+ * Converts a JsonDeserializedHandle to a deeply readonly JsonDeserialized value.
+ */
+export function asDeeplyReadonlyFromJsonHandle<T>(
+	value: OpaqueJsonDeserialized<T>,
+): DeepReadonly<JsonDeserialized<T>> {
+	return asDeeplyReadonly(unbrandJson(value));
 }
diff --git a/packages/framework/presence/src/latestMapValueManager.ts b/packages/framework/presence/src/latestMapValueManager.ts
index 17e17bf6b8f6..6a2f066c440f 100644
--- a/packages/framework/presence/src/latestMapValueManager.ts
+++ b/packages/framework/presence/src/latestMapValueManager.ts
@@ -15,6 +15,11 @@ import type {
 import type { BroadcastControls, BroadcastControlSettings } from "./broadcastControls.js";
 import { OptionalBroadcastControl } from "./broadcastControls.js";
 import type { InternalTypes } from "./exposedInternalTypes.js";
+import {
+	asDeeplyReadonlyFromJsonHandle,
+	brandJson,
+	// type InternalUtilityTypes,
+} from "./exposedUtilityTypes.js";
 import type { PostUpdateAction, ValueManager } from "./internalTypes.js";
 import { asDeeplyReadonly, objectEntries, objectKeys } from "./internalUtils.js";
 import type { LatestClientData, LatestData, LatestMetadata } from "./latestValueTypes.js";
@@ -266,12 +271,15 @@ class ValueMapImpl<T, K extends string | number> implements StateMap<K, T> {
 	): void {
 		for (const [key, item] of objectEntries(this.value.items)) {
 			if (item.value !== undefined) {
-				callbackfn(asDeeplyReadonly(item.value), key, this);
+				callbackfn(asDeeplyReadonlyFromJsonHandle(item.value), key, this);
 			}
 		}
 	}
 	public get(key: K): DeepReadonly<JsonDeserialized<T>> | undefined {
-		return asDeeplyReadonly(this.value.items[key]?.value);
+		return this.value.items[key]?.value === undefined
+			? undefined
+			: // eslint-disable-next-line @typescript-eslint/no-non-null-assertion -- ternary ensures this is non-null
+				asDeeplyReadonlyFromJsonHandle(this.value.items[key]!.value!);
 	}
 	public has(key: K): boolean {
 		return this.value.items[key]?.value !== undefined;
@@ -279,9 +287,9 @@ class ValueMapImpl<T, K extends string | number> implements StateMap<K, T> {
 	public set(key: K, value: JsonSerializable<T> & JsonDeserialized<T>): this {
 		if (!(key in this.value.items)) {
 			this.countDefined += 1;
-			this.value.items[key] = { rev: 0, timestamp: 0, value };
+			this.value.items[key] = { rev: 0, timestamp: 0, value: brandJson(value) };
 		}
-		this.updateItem(key, value);
+		this.updateItem(key, brandJson(value));
 		this.emitter.emit("localItemUpdated", { key, value: asDeeplyReadonly(value) });
 		return this;
 	}
@@ -413,7 +421,7 @@ class LatestMapRawValueManagerImpl<
 			const value = item.value;
 			if (value !== undefined) {
 				items.set(key, {
-					value: asDeeplyReadonly(value),
+					value: asDeeplyReadonlyFromJsonHandle(value),
 					metadata: { revision: item.rev, timestamp: item.timestamp },
 				});
 			}
@@ -464,13 +472,13 @@ class LatestMapRawValueManagerImpl<
 			currentState.items[key] = item;
 			const metadata = { revision: item.rev, timestamp: item.timestamp };
 			if (item.value !== undefined) {
-				const itemValue = asDeeplyReadonly(item.value);
+				const itemValue = asDeeplyReadonlyFromJsonHandle(item.value);
 				const updatedItem = {
 					attendee,
 					key,
 					value: itemValue,
 					metadata,
-				};
+				} satisfies LatestMapItemUpdatedClientData<T, Keys>;
 				postUpdateActions.push(() => this.events.emit("remoteItemUpdated", updatedItem));
 				allUpdates.items.set(key, { value: itemValue, metadata });
 			} else if (hadPriorValue !== undefined) {
@@ -539,7 +547,7 @@ export function latestMap<
 			value.items[key] = {
 				rev: 0,
 				timestamp,
-				value: initialValues[key],
+				value: brandJson(initialValues[key]),
 			};
 		}
 	}
diff --git a/packages/framework/presence/src/latestValueManager.ts b/packages/framework/presence/src/latestValueManager.ts
index 090c6f8f8d4b..80d3f5148e2c 100644
--- a/packages/framework/presence/src/latestValueManager.ts
+++ b/packages/framework/presence/src/latestValueManager.ts
@@ -15,12 +15,18 @@ import { shallowCloneObject } from "@fluidframework/core-utils/internal";
 import type { BroadcastControls, BroadcastControlSettings } from "./broadcastControls.js";
 import { OptionalBroadcastControl } from "./broadcastControls.js";
 import type { InternalTypes } from "./exposedInternalTypes.js";
+import {
+	unbrandJson,
+	brandJson,
+	asDeeplyReadonlyFromJsonHandle,
+} from "./exposedUtilityTypes.js";
 import type { PostUpdateAction, ValueManager } from "./internalTypes.js";
 import { asDeeplyReadonly, objectEntries } from "./internalUtils.js";
 import type { LatestClientData, LatestData } from "./latestValueTypes.js";
 import type { Attendee, Presence } from "./presence.js";
 import { datastoreFromHandle, type StateDatastore } from "./stateDatastore.js";
 import { brandIVM } from "./valueManager.js";
+import type { OpaqueJsonDeserialized } from "@fluidframework/container-runtime-definitions/internal";
 
 /**
  * @sealed
@@ -112,13 +118,13 @@ class LatestValueManagerImpl<T, Key extends string>
 	}
 
 	public get local(): DeepReadonly<JsonDeserialized<T>> {
-		return asDeeplyReadonly(this.value.value);
+		return asDeeplyReadonlyFromJsonHandle(this.value.value);
 	}
 
 	public set local(value: JsonSerializable<T> & JsonDeserialized<T>) {
 		this.value.rev += 1;
 		this.value.timestamp = Date.now();
-		this.value.value = value;
+		this.value.value = brandJson(value);
 		this.datastore.localUpdate(this.key, this.value, {
 			allowableUpdateLatencyMs: this.controls.allowableUpdateLatencyMs,
 		});
@@ -132,7 +138,7 @@ class LatestValueManagerImpl<T, Key extends string>
 			if (attendeeId !== allKnownStates.self) {
 				yield {
 					attendee: this.datastore.lookupClient(attendeeId),
-					value: asDeeplyReadonly(value.value),
+					value: asDeeplyReadonly(unbrandJson(value.value)),
 					metadata: { revision: value.rev, timestamp: value.timestamp },
 				};
 			}
@@ -153,7 +159,7 @@ class LatestValueManagerImpl<T, Key extends string>
 			throw new Error("No entry for clientId");
 		}
 		return {
-			value: asDeeplyReadonly(clientState.value),
+			value: asDeeplyReadonly(unbrandJson(clientState.value)),
 			metadata: { revision: clientState.rev, timestamp: Date.now() },
 		};
 	}
@@ -174,7 +180,7 @@ class LatestValueManagerImpl<T, Key extends string>
 			() =>
 				this.events.emit("remoteUpdated", {
 					attendee,
-					value: asDeeplyReadonly(value.value),
+					value: asDeeplyReadonly(unbrandJson(value.value)),
 					metadata: { revision: value.rev, timestamp: value.timestamp },
 				}),
 		];
@@ -211,10 +217,15 @@ export function latest<T extends object | null, Key extends string = string>(
 
 	// Latest takes ownership of the initial local value but makes a shallow
 	// copy for basic protection.
+	const internalValue =
+		local === null
+			? (local as unknown as OpaqueJsonDeserialized<T>)
+			: // FIXME: Why isn't this directly castable?
+				(shallowCloneObject(local) as unknown as OpaqueJsonDeserialized<T>);
 	const value: InternalTypes.ValueRequiredState<T> = {
 		rev: 0,
 		timestamp: Date.now(),
-		value: local === null ? local : shallowCloneObject(local),
+		value: internalValue,
 	};
 	const factory = (
 		key: Key,
diff --git a/packages/framework/presence/src/notificationsManager.ts b/packages/framework/presence/src/notificationsManager.ts
index 12857b260599..5611402b04b9 100644
--- a/packages/framework/presence/src/notificationsManager.ts
+++ b/packages/framework/presence/src/notificationsManager.ts
@@ -8,11 +8,12 @@ import type { Listeners, Listenable, Off } from "@fluidframework/core-interfaces
 import type { JsonTypeWith } from "@fluidframework/core-interfaces/internal";
 
 import type { InternalTypes } from "./exposedInternalTypes.js";
-import type { InternalUtilityTypes } from "./exposedUtilityTypes.js";
+import { unbrandJson, type InternalUtilityTypes } from "./exposedUtilityTypes.js";
 import type { PostUpdateAction, ValueManager } from "./internalTypes.js";
 import type { Attendee, PresenceWithNotifications as Presence } from "./presence.js";
 import { datastoreFromHandle, type StateDatastore } from "./stateDatastore.js";
 import { brandIVM } from "./valueManager.js";
+import type { OpaqueJsonDeserialized } from "@fluidframework/container-runtime-definitions/internal";
 
 /**
  * @sealed
@@ -177,7 +178,11 @@ class NotificationsManagerImpl<
 				{
 					rev: 0,
 					timestamp: 0,
-					value: { name, args: [...(args as JsonTypeWith<never>[])] },
+					value: {
+						name,
+						args: [...(args as JsonTypeWith<never>[])],
+						// FIXME: Why doesn't as cast work?
+					} as unknown as OpaqueJsonDeserialized<InternalTypes.NotificationType>,
 					ignoreUnmonitored: true,
 				},
 				// This is a notification, so we want to send it immediately.
@@ -190,7 +195,11 @@ class NotificationsManagerImpl<
 				{
 					rev: 0,
 					timestamp: 0,
-					value: { name, args: [...(args as JsonTypeWith<never>[])] },
+					value: {
+						name,
+						args: [...(args as JsonTypeWith<never>[])],
+						// FIXME: Why doesn't as cast work?
+					} as unknown as OpaqueJsonDeserialized<InternalTypes.NotificationType>,
 					ignoreUnmonitored: true,
 				},
 				// This is a notification, so we want to send it immediately.
@@ -237,12 +246,13 @@ class NotificationsManagerImpl<
 		_received: number,
 		value: InternalTypes.ValueRequiredState<InternalTypes.NotificationType>,
 	): PostUpdateAction[] {
+		const unbrandedValue = unbrandJson(value.value);
 		const postUpdateActions: PostUpdateAction[] = [];
-		const eventName = value.value.name as keyof Listeners<NotificationSubscriptions<T>>;
+		const eventName = unbrandedValue.name as keyof Listeners<NotificationSubscriptions<T>>;
 		if (this.notificationsInternal.hasListeners(eventName)) {
 			// Without schema validation, we don't know that the args are the correct type.
 			// For now we assume the user is sending the correct types and there is no corruption along the way.
-			const args = [attendee, ...value.value.args] as Parameters<
+			const args = [attendee, ...unbrandedValue.args] as Parameters<
 				NotificationSubscriptions<T>[typeof eventName]
 			>;
 			postUpdateActions.push(() => this.notificationsInternal.emit(eventName, ...args));
@@ -250,9 +260,9 @@ class NotificationsManagerImpl<
 			postUpdateActions.push(() =>
 				this.events.emit(
 					"unattendedNotification",
-					value.value.name,
+					unbrandedValue.name,
 					attendee,
-					...value.value.args,
+					...unbrandedValue.args,
 				),
 			);
 		}
diff --git a/packages/framework/presence/src/presenceDatastoreManager.ts b/packages/framework/presence/src/presenceDatastoreManager.ts
index bf566a404b01..78ecdbd309e9 100644
--- a/packages/framework/presence/src/presenceDatastoreManager.ts
+++ b/packages/framework/presence/src/presenceDatastoreManager.ts
@@ -167,6 +167,9 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 		this.runtime.submitSignal({
 			type: joinMessageType,
 			content: {
+				// FIXME: error TS2353: Object literal may only specify known properties, and 'sendTimestamp' does not exist in
+				// type 'SerializationErrorPerNonPublicProperties'.
+				//// @ts-ignore
 				sendTimestamp: Date.now(),
 				avgLatency: this.averageLatency,
 				data: this.datastore,
@@ -303,6 +306,9 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 			this.datastore["system:presence"].clientToSessionId[clientConnectionId]!;
 
 		const newMessage = {
+			// FIXME: error TS2353: Object literal may only specify known properties, and 'sendTimestamp' does not exist in
+			// type 'SerializationErrorPerNonPublicProperties'.
+			//// @ts-ignore
 			sendTimestamp: Date.now(),
 			avgLatency: this.averageLatency,
 			// isComplete: false,
@@ -320,13 +326,24 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 			},
 		} satisfies OutboundDatastoreUpdateMessage["content"];
 		this.queuedData = undefined;
-		this.runtime.submitSignal({ type: datastoreUpdateMessageType, content: newMessage });
+		this.runtime.submitSignal({
+			type: datastoreUpdateMessageType,
+			// FIXME: error TS2741: Property '"object serialization error"' is missing in type '{ sendTimestamp: number;
+			// avgLatency: number; data: { "system:presence": { clientToSessionId: { [x: string]: { value:
+			// InternalUtilityTypes.OpaqueJsonDeserialized<AttendeeId>; rev: number; timestamp: number; }; }; }; }; }' but
+			// required in type 'SerializationErrorPerNonPublicProperties'.
+			//// @ts-ignore
+			content: newMessage,
+		});
 	}
 
 	private broadcastAllKnownState(): void {
 		this.runtime.submitSignal({
 			type: datastoreUpdateMessageType,
 			content: {
+				// FIXME: error TS2353: Object literal may only specify known properties, and 'sendTimestamp' does not exist in
+				// type 'SerializationErrorPerNonPublicProperties'.
+				//// @ts-ignore
 				sendTimestamp: Date.now(),
 				avgLatency: this.averageLatency,
 				isComplete: true,
@@ -417,6 +434,11 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 					...workspace.internal.processUpdate(
 						received,
 						timeModifier,
+						// FIXME: error TS2345: Argument of type '{ [x: string]: { [x: string & { readonly StableId:
+						// "53172b0d-a3d5-41ea-bd75-b43839c97f5a"; } & { readonly SessionId: "4498f850-e14e-4be9-8db0-89ec00997e58";
+						// } & { readonly AttendeeId: "AttendeeId"; }]: { ...; } | { ...; }; }; } | { ...; }' is not assignable to
+						// parameter of type 'ValueUpdateRecord'.
+						//// @ts-ignore
 						remoteDatastore,
 						message.clientId,
 					),
@@ -428,6 +450,14 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 				// Ensure there is a datastore at this address and get it.
 				const workspaceDatastore = (this.datastore[workspaceAddress] ??= {});
 				for (const [key, remoteAllKnownState] of Object.entries(remoteDatastore)) {
+					// error TS2345: Argument of type '{ [x: string & { readonly StableId: "53172b0d-a3d5-41ea-bd75-b43839c97f5a";
+					// } & { readonly SessionId: "4498f850-e14e-4be9-8db0-89ec00997e58"; } & { readonly AttendeeId: "AttendeeId";
+					// }]: { ...; } | { ...; }; }' is not assignable to parameter of type 'ClientUpdateRecord'.
+					//
+					// 'string & {readonly StableId: "53172b0d-a3d5-41ea-bd75-b43839c97f5a"; } & { readonly SessionId:
+					// "4498f850-e14e-4be9-8db0-89ec00997e58"; } & { readonly AttendeeId: "AttendeeId"; }' and 'AttendeeId' index
+					// signatures are incompatible.
+					//// @ts-ignore
 					mergeUntrackedDatastore(key, remoteAllKnownState, workspaceDatastore, timeModifier);
 				}
 			}
diff --git a/packages/framework/presence/src/systemWorkspace.ts b/packages/framework/presence/src/systemWorkspace.ts
index b4675e4221fe..7582e48f12a6 100644
--- a/packages/framework/presence/src/systemWorkspace.ts
+++ b/packages/framework/presence/src/systemWorkspace.ts
@@ -9,6 +9,7 @@ import { assert } from "@fluidframework/core-utils/internal";
 
 import type { ClientConnectionId } from "./baseTypes.js";
 import type { InternalTypes } from "./exposedInternalTypes.js";
+import { unbrandJson, brandJson } from "./exposedUtilityTypes.js";
 import type { PostUpdateAction } from "./internalTypes.js";
 import type { Attendee, AttendeesEvents, AttendeeId, Presence } from "./presence.js";
 import { AttendeeStatus } from "./presence.js";
@@ -133,7 +134,7 @@ class SystemWorkspaceImpl implements PresenceStatesInternal, SystemWorkspace {
 		for (const [clientConnectionId, value] of Object.entries(
 			remoteDatastore.clientToSessionId,
 		)) {
-			const attendeeId = value.value;
+			const attendeeId = unbrandJson(value.value);
 			const { attendee, isJoining } = this.ensureAttendee(
 				attendeeId,
 				clientConnectionId,
@@ -169,7 +170,7 @@ class SystemWorkspaceImpl implements PresenceStatesInternal, SystemWorkspace {
 		this.datastore.clientToSessionId[clientConnectionId] = {
 			rev: this.selfAttendee.order++,
 			timestamp: Date.now(),
-			value: this.selfAttendee.attendeeId,
+			value: brandJson(this.selfAttendee.attendeeId),
 		};
 
 		// Mark 'Connected' remote attendees connections as stale
@@ -306,7 +307,8 @@ export function createSystemWorkspace(
 	return {
 		workspace,
 		statesEntry: {
-			internal: workspace,
+			// FIXME: Cast shouldn't be needed
+			internal: workspace as PresenceStatesInternal,
 			public: undefined as unknown as AnyWorkspace<StatesWorkspaceSchema>,
 		},
 	};
diff --git a/packages/runtime/container-runtime-definitions/src/containerExtension.ts b/packages/runtime/container-runtime-definitions/src/containerExtension.ts
index 28f40e031937..261f6ee8ae1b 100644
--- a/packages/runtime/container-runtime-definitions/src/containerExtension.ts
+++ b/packages/runtime/container-runtime-definitions/src/containerExtension.ts
@@ -57,7 +57,13 @@ export type ExtensionMessage<
  * @internal
  */
 export type OutboundExtensionMessage<TMessage extends TypedMessage = TypedMessage> =
-	ExtensionMessage<{ type: TMessage["type"]; content: JsonSerializable<TMessage["content"]> }>;
+	ExtensionMessage<{
+		type: TMessage["type"];
+		content: JsonSerializable<
+			TMessage["content"],
+			{ AllowExtensionOf: OpaqueJsonDeserialized<TMessage["content"]> }
+		>;
+	}>;
 
 /**
  * Brand for value that has not been verified.
@@ -299,3 +305,16 @@ export interface ContainerExtensionStore {
 		...context: TUseContext
 	): T;
 }
+
+/**
+ * @internal
+ */
+export declare class JsonDeserializedBrand<T> extends BrandedType<T> {
+	private readonly EncodedValue: T;
+	private constructor();
+}
+
+/**
+ * @internal
+ */
+export type OpaqueJsonDeserialized<T> = JsonDeserializedBrand<T>;
diff --git a/packages/runtime/container-runtime-definitions/src/index.ts b/packages/runtime/container-runtime-definitions/src/index.ts
index bf0dc6d1eaae..feb373ab0170 100644
--- a/packages/runtime/container-runtime-definitions/src/index.ts
+++ b/packages/runtime/container-runtime-definitions/src/index.ts
@@ -14,7 +14,9 @@ export type {
 	ExtensionMessage,
 	ExtensionRuntimeProperties,
 	InboundExtensionMessage,
+	JsonDeserializedBrand,
 	OutboundExtensionMessage,
+	OpaqueJsonDeserialized,
 	RawInboundExtensionMessage,
 	UnverifiedBrand,
 	VerifiedInboundExtensionMessage,