diff --git a/packages/framework/presence/api-report/presence.alpha.api.md b/packages/framework/presence/api-report/presence.alpha.api.md
index 2ed0ce115573..9d3bce57488e 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 {
@@ -128,26 +128,12 @@ export namespace InternalTypes {
     }
 }
 
-// @alpha @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;
-    // @system
-    export type JsonDeserializedParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonDeserialized<P> : never;
-    // @system
-    export type JsonSerializableParameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? JsonSerializable<P> : never;
-    // @system
-    export type NotificationListeners<E> = {
-        [P in string & keyof E as IsNotificationListener<E[P]> extends true ? P : never]: E[P];
-    };
-}
-
 // @beta
 export function latest<T extends object | null, Key extends string = string>(args: LatestArguments<T>): InternalTypes.ManagerFactory<Key, InternalTypes.ValueRequiredState<T>, LatestRaw<T>>;
 
-// @beta
+// @beta @input
 export interface LatestArguments<T extends object | null> {
-    local: JsonSerializable<T> & JsonDeserialized<T> & (object | null);
+    local: JsonSerializable<T> & JsonDeserialized<T>;
     settings?: BroadcastControlSettings | undefined;
 }
 
@@ -159,16 +145,16 @@ export interface LatestClientData<T> extends LatestData<T> {
 // @beta @sealed
 export interface LatestData<T> {
     metadata: LatestMetadata;
-    value: DeepReadonly<JsonDeserialized<T>>;
+    value: DeepReadonly<JsonDeserialized_2<T>>;
 }
 
 // @beta
 export function latestMap<T, Keys extends string | number = string | number, RegistrationKey extends string = string>(args?: LatestMapArguments<T, Keys>): InternalTypes.ManagerFactory<RegistrationKey, InternalTypes.MapValueState<T, Keys>, LatestMapRaw<T, Keys>>;
 
-// @beta
+// @beta @input
 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;
 }
@@ -210,7 +196,7 @@ 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
@@ -234,8 +220,8 @@ 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_2<JsonDeserialized<T>>;
+    set local(value: JsonDeserialized<T>);
     readonly presence: Presence;
 }
 
@@ -243,7 +229,7 @@ export interface LatestRaw<T> {
 export interface LatestRawEvents<T> {
     // @eventProperty
     localUpdated: (update: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly_2<JsonSerializable<T> & JsonDeserialized<T>>;
     }) => void;
     // @eventProperty
     remoteUpdated: (update: LatestClientData<T>) => void;
@@ -251,8 +237,8 @@ export interface LatestRawEvents<T> {
 
 // @alpha @sealed
 export interface NotificationEmitter<E extends InternalUtilityTypes.NotificationListeners<E>> {
-    broadcast<K extends string & keyof InternalUtilityTypes.NotificationListeners<E>>(notificationName: K, ...args: Parameters<E[K]>): void;
-    unicast<K extends string & keyof InternalUtilityTypes.NotificationListeners<E>>(notificationName: K, targetAttendee: Attendee, ...args: Parameters<E[K]>): void;
+    broadcast<K extends keyof InternalUtilityTypes.NotificationListeners<E>>(notificationName: K, ...args: Parameters<E[K]>): void;
+    unicast<K extends keyof InternalUtilityTypes.NotificationListeners<E>>(notificationName: K, targetAttendee: Attendee, ...args: Parameters<E[K]>): void;
 }
 
 // @alpha @sealed
@@ -335,11 +321,11 @@ export const StateFactory: {
 export interface StateMap<K extends string | number, V> {
     clear(): void;
     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;
     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;
     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 240e944302dd..7152ae3e25f9 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 {
@@ -118,9 +118,9 @@ export namespace InternalTypes {
 // @beta
 export function latest<T extends object | null, Key extends string = string>(args: LatestArguments<T>): InternalTypes.ManagerFactory<Key, InternalTypes.ValueRequiredState<T>, LatestRaw<T>>;
 
-// @beta
+// @beta @input
 export interface LatestArguments<T extends object | null> {
-    local: JsonSerializable<T> & JsonDeserialized<T> & (object | null);
+    local: JsonSerializable<T> & JsonDeserialized<T>;
     settings?: BroadcastControlSettings | undefined;
 }
 
@@ -132,16 +132,16 @@ export interface LatestClientData<T> extends LatestData<T> {
 // @beta @sealed
 export interface LatestData<T> {
     metadata: LatestMetadata;
-    value: DeepReadonly<JsonDeserialized<T>>;
+    value: DeepReadonly<JsonDeserialized_2<T>>;
 }
 
 // @beta
 export function latestMap<T, Keys extends string | number = string | number, RegistrationKey extends string = string>(args?: LatestMapArguments<T, Keys>): InternalTypes.ManagerFactory<RegistrationKey, InternalTypes.MapValueState<T, Keys>, LatestMapRaw<T, Keys>>;
 
-// @beta
+// @beta @input
 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;
 }
@@ -183,7 +183,7 @@ 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
@@ -207,8 +207,8 @@ 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_2<JsonDeserialized<T>>;
+    set local(value: JsonDeserialized<T>);
     readonly presence: Presence;
 }
 
@@ -216,7 +216,7 @@ export interface LatestRaw<T> {
 export interface LatestRawEvents<T> {
     // @eventProperty
     localUpdated: (update: {
-        value: DeepReadonly<JsonSerializable<T> & JsonDeserialized<T>>;
+        value: DeepReadonly_2<JsonSerializable<T> & JsonDeserialized<T>>;
     }) => void;
     // @eventProperty
     remoteUpdated: (update: LatestClientData<T>) => void;
@@ -253,11 +253,11 @@ export const StateFactory: {
 export interface StateMap<K extends string | number, V> {
     clear(): void;
     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;
     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;
     readonly size: number;
 }
 
diff --git a/packages/framework/presence/src/exposedInternalTypes.ts b/packages/framework/presence/src/exposedInternalTypes.ts
index 46e457098129..801e9499ffef 100644
--- a/packages/framework/presence/src/exposedInternalTypes.ts
+++ b/packages/framework/presence/src/exposedInternalTypes.ts
@@ -6,7 +6,8 @@
 import type {
 	JsonDeserialized,
 	JsonSerializable,
-} from "@fluidframework/core-interfaces/internal/exposedUtilityTypes";
+	OpaqueJsonDeserialized,
+} 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..a80408d75172 100644
--- a/packages/framework/presence/src/exposedUtilityTypes.ts
+++ b/packages/framework/presence/src/exposedUtilityTypes.ts
@@ -7,30 +7,33 @@ import type {
 	InternalUtilityTypes as CoreInternalUtilityTypes,
 	JsonDeserialized,
 	JsonSerializable,
-} from "@fluidframework/core-interfaces/internal/exposedUtilityTypes";
+} from "@fluidframework/core-interfaces/internal";
 
 /**
  * Collection of utility types that are not intended to be used/imported
  * directly outside of this package.
  *
- * @alpha
+ * @internal
  * @system
  */
 // eslint-disable-next-line @typescript-eslint/no-namespace
 export namespace InternalUtilityTypes {
 	/**
-	 * `true` iff the given type is an acceptable shape for a notification.
+	 * `IfListener` iff the given type is an acceptable shape for a notification.
+	 * `Else` otherwise.
 	 *
 	 * @system
 	 */
-	export type IsNotificationListener<Event> = Event extends (...args: infer P) => void
+	export type IfNotificationListener<Event, IfListener, Else> = Event extends (
+		...args: infer P
+	) => void
 		? CoreInternalUtilityTypes.IfSameType<
 				P,
 				JsonSerializable<P> & JsonDeserialized<P>,
-				true,
-				false
+				IfListener,
+				Else
 			>
-		: false;
+		: Else;
 
 	/**
 	 * Used to specify the kinds of notifications emitted by a {@link NotificationListenable}.
@@ -52,7 +55,7 @@ export namespace InternalUtilityTypes {
 	 * @system
 	 */
 	export type NotificationListeners<E> = {
-		[P in string & keyof E as IsNotificationListener<E[P]> extends true ? P : never]: E[P];
+		[P in keyof E as IfNotificationListener<E[P], P, never>]: E[P];
 	};
 
 	/**
@@ -60,7 +63,7 @@ export namespace InternalUtilityTypes {
 	 *
 	 * @system
 	 */
-	export type JsonDeserializedParameters<T extends (...args: any) => any> = T extends (
+	export type JsonDeserializedParameters<T extends (...args: any[]) => any> = T extends (
 		...args: infer P
 	) => any
 		? JsonDeserialized<P>
@@ -71,7 +74,7 @@ export namespace InternalUtilityTypes {
 	 *
 	 * @system
 	 */
-	export type JsonSerializableParameters<T extends (...args: any) => any> = T extends (
+	export type JsonSerializableParameters<T extends (...args: any[]) => any> = T extends (
 		...args: infer P
 	) => any
 		? JsonSerializable<P>
diff --git a/packages/framework/presence/src/internalUtils.ts b/packages/framework/presence/src/internalUtils.ts
index eb741cbe8e46..8045b3bf4a6a 100644
--- a/packages/framework/presence/src/internalUtils.ts
+++ b/packages/framework/presence/src/internalUtils.ts
@@ -3,7 +3,13 @@
  * Licensed under the MIT License.
  */
 
-import type { DeepReadonly } from "@fluidframework/core-interfaces/internal";
+import type {
+	DeepReadonly,
+	JsonDeserialized,
+	JsonSerializable,
+	OpaqueJsonDeserialized,
+	OpaqueJsonSerializable,
+} from "@fluidframework/core-interfaces/internal";
 
 /**
  * Returns union of types of values in a record.
@@ -75,8 +81,39 @@ export function getOrCreateRecord<const K extends string | number | symbol, cons
 }
 
 /**
- * Do nothing helper to apply deep immutability to a value's type.
+ * Does nothing helper to apply deep immutability to a value's type.
  */
 export function asDeeplyReadonly<T>(value: T): DeepReadonly<T> {
 	return value as DeepReadonly<T>;
 }
+
+export function asDeeplyReadonlyDeserializedJson<T>(
+	value: OpaqueJsonDeserialized<T>,
+): DeepReadonly<JsonDeserialized<T>>;
+export function asDeeplyReadonlyDeserializedJson<T>(
+	value: OpaqueJsonDeserialized<T> | undefined,
+): DeepReadonly<JsonDeserialized<T>> | undefined;
+/**
+ * Does nothing helper to apply deep immutability to a value's opaque Json type revealing the Json type.
+ */
+export function asDeeplyReadonlyDeserializedJson<T>(
+	value: OpaqueJsonDeserialized<T> | undefined,
+): DeepReadonly<JsonDeserialized<T>> | undefined {
+	return value as DeepReadonly<JsonDeserialized<T>> | undefined;
+}
+
+/**
+ * Does nothing helper to reveal the Json type from a value's opaque Json type.
+ */
+export function asDeserializedJson<T>(value: OpaqueJsonDeserialized<T>): JsonDeserialized<T> {
+	return value as JsonDeserialized<T>;
+}
+
+/**
+ * Does nothing helper to automatically cast Json type to Opaque Json type.
+ */
+export function fullySerializableToOpaqueJson<const T>(
+	value: JsonSerializable<T> & JsonDeserialized<T>,
+): OpaqueJsonSerializable<T> & OpaqueJsonDeserialized<T> {
+	return value as OpaqueJsonSerializable<T> & OpaqueJsonDeserialized<T>;
+}
diff --git a/packages/framework/presence/src/latestMapValueManager.ts b/packages/framework/presence/src/latestMapValueManager.ts
index 44e1adff0f22..22b566785578 100644
--- a/packages/framework/presence/src/latestMapValueManager.ts
+++ b/packages/framework/presence/src/latestMapValueManager.ts
@@ -16,7 +16,13 @@ import type { BroadcastControls, BroadcastControlSettings } from "./broadcastCon
 import { OptionalBroadcastControl } from "./broadcastControls.js";
 import type { InternalTypes } from "./exposedInternalTypes.js";
 import type { PostUpdateAction, ValueManager } from "./internalTypes.js";
-import { asDeeplyReadonly, objectEntries, objectKeys } from "./internalUtils.js";
+import {
+	asDeeplyReadonly,
+	objectEntries,
+	objectKeys,
+	fullySerializableToOpaqueJson,
+	asDeeplyReadonlyDeserializedJson,
+} from "./internalUtils.js";
 import type { LatestClientData, LatestData, LatestMetadata } from "./latestValueTypes.js";
 import type { AttendeeId, Attendee, Presence, SpecificAttendee } from "./presence.js";
 import { datastoreFromHandle, type StateDatastore } from "./stateDatastore.js";
@@ -286,23 +292,31 @@ 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(asDeeplyReadonlyDeserializedJson(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
+				asDeeplyReadonlyDeserializedJson(this.value.items[key]!.value!);
 	}
 	public has(key: K): boolean {
 		return this.value.items[key]?.value !== undefined;
 	}
-	public set(key: K, value: JsonSerializable<T> & JsonDeserialized<T>): this {
+	public set(key: K, inValue: JsonSerializable<T> & JsonDeserialized<T>): this {
+		const value = fullySerializableToOpaqueJson(inValue);
 		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,
+			} satisfies InternalTypes.ValueOptionalState<T>;
 		}
 		this.updateItem(key, value);
-		this.emitter.emit("localItemUpdated", { key, value: asDeeplyReadonly(value) });
+		this.emitter.emit("localItemUpdated", { key, value: asDeeplyReadonly(inValue) });
 		return this;
 	}
 	public get size(): number {
@@ -433,7 +447,7 @@ class LatestMapRawValueManagerImpl<
 			const value = item.value;
 			if (value !== undefined) {
 				items.set(key, {
-					value: asDeeplyReadonly(value),
+					value: asDeeplyReadonlyDeserializedJson(value),
 					metadata: { revision: item.rev, timestamp: item.timestamp },
 				});
 			}
@@ -484,13 +498,13 @@ 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 = asDeeplyReadonlyDeserializedJson(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) {
@@ -512,6 +526,7 @@ class LatestMapRawValueManagerImpl<
 /**
  * Arguments that are passed to the {@link StateFactory.latestMap} function.
  *
+ * @input
  * @beta
  */
 export interface LatestMapArguments<T, Keys extends string | number = string | number> {
@@ -559,7 +574,7 @@ export function latestMap<
 			value.items[key] = {
 				rev: 0,
 				timestamp,
-				value: initialValues[key],
+				value: fullySerializableToOpaqueJson(initialValues[key]),
 			};
 		}
 	}
diff --git a/packages/framework/presence/src/latestValueManager.ts b/packages/framework/presence/src/latestValueManager.ts
index 08d0fc16732c..b4aebc456867 100644
--- a/packages/framework/presence/src/latestValueManager.ts
+++ b/packages/framework/presence/src/latestValueManager.ts
@@ -9,14 +9,19 @@ import type {
 	DeepReadonly,
 	JsonDeserialized,
 	JsonSerializable,
-} from "@fluidframework/core-interfaces/internal/exposedUtilityTypes";
+} from "@fluidframework/core-interfaces/internal";
 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 type { PostUpdateAction, ValueManager } from "./internalTypes.js";
-import { asDeeplyReadonly, objectEntries } from "./internalUtils.js";
+import {
+	asDeeplyReadonly,
+	asDeeplyReadonlyDeserializedJson,
+	fullySerializableToOpaqueJson,
+	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";
@@ -78,7 +83,7 @@ export interface LatestRaw<T> {
 	 * setting, if needed. No comparison is done to detect changes; all sets are transmitted.
 	 */
 	get local(): DeepReadonly<JsonDeserialized<T>>;
-	set local(value: JsonSerializable<T> & JsonDeserialized<T>);
+	set local(value: JsonDeserialized<T>);
 
 	/**
 	 * Iterable access to remote clients' values.
@@ -114,18 +119,20 @@ class LatestValueManagerImpl<T, Key extends string>
 	}
 
 	public get local(): DeepReadonly<JsonDeserialized<T>> {
-		return asDeeplyReadonly(this.value.value);
+		return asDeeplyReadonlyDeserializedJson(this.value.value);
 	}
 
-	public set local(value: JsonSerializable<T> & JsonDeserialized<T>) {
+	public set local(value: JsonDeserialized<T> & JsonSerializable<T>) {
 		this.value.rev += 1;
 		this.value.timestamp = Date.now();
-		this.value.value = value;
+		this.value.value = fullySerializableToOpaqueJson(value);
 		this.datastore.localUpdate(this.key, this.value, {
 			allowableUpdateLatencyMs: this.controls.allowableUpdateLatencyMs,
 		});
 
-		this.events.emit("localUpdated", { value: asDeeplyReadonly(value) });
+		this.events.emit("localUpdated", {
+			value: asDeeplyReadonly(value),
+		});
 	}
 
 	public *getRemotes(): IterableIterator<LatestClientData<T>> {
@@ -134,7 +141,7 @@ class LatestValueManagerImpl<T, Key extends string>
 			if (attendeeId !== allKnownStates.self) {
 				yield {
 					attendee: this.datastore.presence.attendees.getAttendee(attendeeId),
-					value: asDeeplyReadonly(value.value),
+					value: asDeeplyReadonlyDeserializedJson(value.value),
 					metadata: { revision: value.rev, timestamp: value.timestamp },
 				};
 			}
@@ -155,7 +162,7 @@ class LatestValueManagerImpl<T, Key extends string>
 			throw new Error("No entry for clientId");
 		}
 		return {
-			value: asDeeplyReadonly(clientState.value),
+			value: asDeeplyReadonlyDeserializedJson(clientState.value),
 			metadata: { revision: clientState.rev, timestamp: Date.now() },
 		};
 	}
@@ -176,24 +183,35 @@ class LatestValueManagerImpl<T, Key extends string>
 			() =>
 				this.events.emit("remoteUpdated", {
 					attendee,
-					value: asDeeplyReadonly(value.value),
+					value: asDeeplyReadonlyDeserializedJson(value.value),
 					metadata: { revision: value.rev, timestamp: value.timestamp },
 				}),
 		];
 	}
 }
 
+/**
+ * Shallow clone an object that might be null.
+ *
+ * @param value - The object to clone
+ * @returns A shallow clone of the input value
+ * @internal
+ */
+export function shallowCloneNullableObject<T extends object | null>(value: T): T {
+	return value === null ? value : shallowCloneObject(value);
+}
+
 /**
  * Arguments that are passed to the {@link StateFactory.latest} function.
  *
+ * @input
  * @beta
  */
 export interface LatestArguments<T extends object | null> {
 	/**
 	 * The initial value of the local state.
 	 */
-	// eslint-disable-next-line @rushstack/no-new-null
-	local: JsonSerializable<T> & JsonDeserialized<T> & (object | null);
+	local: JsonSerializable<T> & JsonDeserialized<T>;
 
 	/**
 	 * See {@link BroadcastControlSettings}.
@@ -213,10 +231,11 @@ 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 opaqueLocal = fullySerializableToOpaqueJson<T>(local);
 	const value: InternalTypes.ValueRequiredState<T> = {
 		rev: 0,
 		timestamp: Date.now(),
-		value: local === null ? local : shallowCloneObject(local),
+		value: shallowCloneNullableObject(opaqueLocal),
 	};
 	const factory = (
 		key: Key,
diff --git a/packages/framework/presence/src/notificationsManager.ts b/packages/framework/presence/src/notificationsManager.ts
index 12857b260599..49d2d24c3c52 100644
--- a/packages/framework/presence/src/notificationsManager.ts
+++ b/packages/framework/presence/src/notificationsManager.ts
@@ -10,6 +10,7 @@ import type { JsonTypeWith } from "@fluidframework/core-interfaces/internal";
 import type { InternalTypes } from "./exposedInternalTypes.js";
 import type { InternalUtilityTypes } from "./exposedUtilityTypes.js";
 import type { PostUpdateAction, ValueManager } from "./internalTypes.js";
+import { asDeserializedJson, fullySerializableToOpaqueJson } from "./internalUtils.js";
 import type { Attendee, PresenceWithNotifications as Presence } from "./presence.js";
 import { datastoreFromHandle, type StateDatastore } from "./stateDatastore.js";
 import { brandIVM } from "./valueManager.js";
@@ -100,7 +101,7 @@ export interface NotificationEmitter<E extends InternalUtilityTypes.Notification
 	 * @param notificationName - the name of the notification to fire
 	 * @param args - the arguments sent with the notification
 	 */
-	broadcast<K extends string & keyof InternalUtilityTypes.NotificationListeners<E>>(
+	broadcast<K extends keyof InternalUtilityTypes.NotificationListeners<E>>(
 		notificationName: K,
 		...args: Parameters<E[K]>
 	): void;
@@ -111,7 +112,7 @@ export interface NotificationEmitter<E extends InternalUtilityTypes.Notification
 	 * @param targetAttendee - the single attendee to notify
 	 * @param args - the arguments sent with the notification
 	 */
-	unicast<K extends string & keyof InternalUtilityTypes.NotificationListeners<E>>(
+	unicast<K extends keyof InternalUtilityTypes.NotificationListeners<E>>(
 		notificationName: K,
 		targetAttendee: Attendee,
 		...args: Parameters<E[K]>
@@ -171,26 +172,32 @@ class NotificationsManagerImpl<
 	public readonly events = createEmitter<NotificationsManagerEvents>();
 
 	public readonly emit: NotificationEmitter<T> = {
-		broadcast: (name, ...args) => {
+		broadcast: (name: string, ...args) => {
 			this.datastore.localUpdate(
 				this.key,
 				{
 					rev: 0,
 					timestamp: 0,
-					value: { name, args: [...(args as JsonTypeWith<never>[])] },
+					value: fullySerializableToOpaqueJson({
+						name,
+						args: [...(args as JsonTypeWith<never>[])],
+					}),
 					ignoreUnmonitored: true,
 				},
 				// This is a notification, so we want to send it immediately.
 				{ allowableUpdateLatencyMs: 0 },
 			);
 		},
-		unicast: (name, targetAttendee, ...args) => {
+		unicast: (name: string, targetAttendee, ...args) => {
 			this.datastore.localUpdate(
 				this.key,
 				{
 					rev: 0,
 					timestamp: 0,
-					value: { name, args: [...(args as JsonTypeWith<never>[])] },
+					value: fullySerializableToOpaqueJson({
+						name,
+						args: [...(args as JsonTypeWith<never>[])],
+					}),
 					ignoreUnmonitored: true,
 				},
 				// This is a notification, so we want to send it immediately.
@@ -202,7 +209,6 @@ class NotificationsManagerImpl<
 	// Workaround for types
 	private readonly notificationsInternal = createEmitter<NotificationSubscriptions<T>>();
 
-	// @ts-expect-error TODO
 	public readonly notifications: NotificationListenable<T> = this.notificationsInternal;
 
 	public constructor(
@@ -235,25 +241,21 @@ class NotificationsManagerImpl<
 	public update(
 		attendee: Attendee,
 		_received: number,
-		value: InternalTypes.ValueRequiredState<InternalTypes.NotificationType>,
+		updateValue: InternalTypes.ValueRequiredState<InternalTypes.NotificationType>,
 	): PostUpdateAction[] {
 		const postUpdateActions: PostUpdateAction[] = [];
-		const eventName = value.value.name as keyof Listeners<NotificationSubscriptions<T>>;
+		const value = asDeserializedJson(updateValue.value);
+		const eventName = value.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, ...value.args] as Parameters<
 				NotificationSubscriptions<T>[typeof eventName]
 			>;
 			postUpdateActions.push(() => this.notificationsInternal.emit(eventName, ...args));
 		} else {
 			postUpdateActions.push(() =>
-				this.events.emit(
-					"unattendedNotification",
-					value.value.name,
-					attendee,
-					...value.value.args,
-				),
+				this.events.emit("unattendedNotification", value.name, attendee, ...value.args),
 			);
 		}
 		return postUpdateActions;
diff --git a/packages/framework/presence/src/presenceDatastoreManager.ts b/packages/framework/presence/src/presenceDatastoreManager.ts
index bf1e4b696051..9ebe2fa192aa 100644
--- a/packages/framework/presence/src/presenceDatastoreManager.ts
+++ b/packages/framework/presence/src/presenceDatastoreManager.ts
@@ -177,7 +177,8 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 			content: {
 				sendTimestamp: Date.now(),
 				avgLatency: this.averageLatency,
-				data: this.datastore,
+				// FIXME: remove cast
+				data: this.datastore as any,
 				updateProviders,
 			},
 		});
@@ -327,7 +328,10 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 			},
 		} satisfies OutboundDatastoreUpdateMessage["content"];
 		this.queuedData = undefined;
-		this.runtime.submitSignal({ type: datastoreUpdateMessageType, content: newMessage });
+		this.runtime.submitSignal({
+			type: datastoreUpdateMessageType,
+			content: newMessage,
+		});
 	}
 
 	private broadcastAllKnownState(): void {
@@ -337,7 +341,8 @@ export class PresenceDatastoreManagerImpl implements PresenceDatastoreManager {
 				sendTimestamp: Date.now(),
 				avgLatency: this.averageLatency,
 				isComplete: true,
-				data: this.datastore,
+				// FIXME: remove cast
+				data: this.datastore as any,
 			},
 		});
 		this.refreshBroadcastRequested = false;
diff --git a/packages/framework/presence/src/systemWorkspace.ts b/packages/framework/presence/src/systemWorkspace.ts
index 342de7818f5e..a483d1869824 100644
--- a/packages/framework/presence/src/systemWorkspace.ts
+++ b/packages/framework/presence/src/systemWorkspace.ts
@@ -10,6 +10,7 @@ import { assert } from "@fluidframework/core-utils/internal";
 import type { ClientConnectionId } from "./baseTypes.js";
 import type { InternalTypes } from "./exposedInternalTypes.js";
 import type { PostUpdateAction } from "./internalTypes.js";
+import { asDeserializedJson, fullySerializableToOpaqueJson } from "./internalUtils.js";
 import type { Attendee, AttendeesEvents, AttendeeId, Presence } from "./presence.js";
 import { AttendeeStatus } from "./presence.js";
 import type { PresenceStatesInternal } from "./presenceStates.js";
@@ -131,7 +132,7 @@ class SystemWorkspaceImpl implements PresenceStatesInternal, SystemWorkspace {
 		for (const [clientConnectionId, value] of Object.entries(
 			remoteDatastore.clientToSessionId,
 		)) {
-			const attendeeId = value.value;
+			const attendeeId = asDeserializedJson(value.value);
 			const { attendee, isJoining } = this.ensureAttendee(
 				attendeeId,
 				clientConnectionId,
@@ -146,8 +147,7 @@ class SystemWorkspaceImpl implements PresenceStatesInternal, SystemWorkspace {
 				postUpdateActions.push(() => this.events.emit("attendeeConnected", attendee));
 			}
 
-			const knownSessionId: InternalTypes.ValueRequiredState<AttendeeId> | undefined =
-				this.datastore.clientToSessionId[clientConnectionId];
+			const knownSessionId = this.datastore.clientToSessionId[clientConnectionId];
 			if (knownSessionId === undefined) {
 				this.datastore.clientToSessionId[clientConnectionId] = value;
 			} else {
@@ -167,7 +167,7 @@ class SystemWorkspaceImpl implements PresenceStatesInternal, SystemWorkspace {
 		this.datastore.clientToSessionId[clientConnectionId] = {
 			rev: this.selfAttendee.order++,
 			timestamp: Date.now(),
-			value: this.selfAttendee.attendeeId,
+			value: fullySerializableToOpaqueJson(this.selfAttendee.attendeeId),
 		};
 
 		// Mark 'Connected' remote attendees connections as stale
diff --git a/packages/framework/presence/src/test/latestValueManager.spec.ts b/packages/framework/presence/src/test/latestValueManager.spec.ts
index 7afc32adf988..f1cabca79eb2 100644
--- a/packages/framework/presence/src/test/latestValueManager.spec.ts
+++ b/packages/framework/presence/src/test/latestValueManager.spec.ts
@@ -84,6 +84,22 @@ describe("Presence", () => {
 				assert.deepStrictEqual(workspace.states.nullable.local, null);
 			});
 
+			it("can set and get inferred nullable type as initial value", () => {
+				// Setup
+				// Use a function to generate the initial value so that TypeScript
+				// can't statically infer the type as exactly null.
+				function generateInitialValue(): { x: number; y: number } | null {
+					return { x: 0, y: 0 };
+				}
+				const initialValue = generateInitialValue();
+				// Act
+				const workspace = presence.states.getWorkspace(testWorkspaceName, {
+					nullable: StateFactory.latest({ local: initialValue }),
+				});
+				// Verify
+				assert.deepStrictEqual(workspace.states.nullable.local, initialValue);
+			});
+
 			it(".presence provides Presence it was created under", () => {
 				const workspace = presence.states.getWorkspace(testWorkspaceName, {
 					camera: StateFactory.latest({ local: { x: 0, y: 0, z: 0 } }),