diff --git a/packages/svelte/src/reactivity/map.js b/packages/svelte/src/reactivity/map.js
index 48d06a05a7..5ff327a7f4 100644
--- a/packages/svelte/src/reactivity/map.js
+++ b/packages/svelte/src/reactivity/map.js
@@ -3,6 +3,9 @@ import { DEV } from 'esm-env';
 import { set, source, state, increment } from '../internal/client/reactivity/sources.js';
 import { label, tag } from '../internal/client/dev/tracing.js';
 import { get, update_version } from '../internal/client/runtime.js';
+import { async_mode_flag } from '../internal/flags/index.js';
+
+const MISSING = Symbol('missing');
 
 /**
  * A reactive version of the built-in [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) object.
@@ -51,10 +54,10 @@ import { get, update_version } from '../internal/client/runtime.js';
  * @extends {Map<K, V>}
  */
 export class SvelteMap extends Map {
-	/** @type {Map<K, Source<number>>} */
+	/** @type {Map<K, Source<V>>} */
 	#sources = new Map();
-	#version = state(0);
-	#size = state(0);
+	/** @type {Source<Map<K, V>>} */
+	#items;
 	#update_version = update_version || -1;
 
 	/**
@@ -63,19 +66,16 @@ export class SvelteMap extends Map {
 	constructor(value) {
 		super();
 
-		if (DEV) {
-			// If the value is invalid then the native exception will fire here
-			value = new Map(value);
+		this.#items = state(new Map(value));
 
-			tag(this.#version, 'SvelteMap version');
-			tag(this.#size, 'SvelteMap.size');
+		var sources = this.#sources;
+
+		for (const [key, value] of this.#items.v) {
+			sources.set(key, this.#source(value));
 		}
 
-		if (value) {
-			for (var [key, v] of value) {
-				super.set(key, v);
-			}
-			this.#size.v = super.size;
+		if (DEV) {
+			tag(this.#items, 'SvelteMap items');
 		}
 	}
 
@@ -98,24 +98,27 @@ export class SvelteMap extends Map {
 		var s = sources.get(key);
 
 		if (s === undefined) {
-			if (super.has(key)) {
-				s = this.#source(0);
-
-				if (DEV) {
-					tag(s, `SvelteMap get(${label(key)})`);
-				}
-
-				sources.set(key, s);
-			} else {
-				// We should always track the version in case
-				// the Set ever gets this value in the future.
-				get(this.#version);
+			if (!async_mode_flag) {
+				// If the value doesn't exist, track the version in case it's added later
+				// but don't create sources willy-nilly to track all possible values
+				get(this.#items);
 				return false;
 			}
+
+			var items = get(this.#items);
+			var value = /** @type {V} */ (items.has(key) ? items.get(key) : (MISSING));
+
+			s = this.#source(value);
+
+			if (DEV) {
+				tag(s, `SvelteSet has(${label(value)})`);
+			}
+
+			sources.set(key, s);
 		}
 
-		get(s);
-		return true;
+		var value = get(s);
+		return value !== MISSING;
 	}
 
 	/**
@@ -123,8 +126,9 @@ export class SvelteMap extends Map {
 	 * @param {any} [this_arg]
 	 */
 	forEach(callbackfn, this_arg) {
-		this.#read_all();
-		super.forEach(callbackfn, this_arg);
+		for (const [key, value] of this.entries()) {
+			callbackfn(value, key, this);
+		}
 	}
 
 	/** @param {K} key */
@@ -133,24 +137,15 @@ export class SvelteMap extends Map {
 		var s = sources.get(key);
 
 		if (s === undefined) {
-			if (super.has(key)) {
-				s = this.#source(0);
-
-				if (DEV) {
-					tag(s, `SvelteMap get(${label(key)})`);
-				}
-
-				sources.set(key, s);
-			} else {
-				// We should always track the version in case
-				// the Set ever gets this value in the future.
-				get(this.#version);
-				return undefined;
-			}
+			// We should always track the version in case
+			// the Set ever gets this value in the future.
+			var items = get(this.#items);
+			return items.get(key);
 		}
 
-		get(s);
-		return super.get(key);
+		var value = get(s);
+
+		return value === MISSING ? undefined : value;
 	}
 
 	/**
@@ -160,107 +155,86 @@ export class SvelteMap extends Map {
 	set(key, value) {
 		var sources = this.#sources;
 		var s = sources.get(key);
-		var prev_res = super.get(key);
-		var res = super.set(key, value);
-		var version = this.#version;
 
-		if (s === undefined) {
-			s = this.#source(0);
+		if (s !== undefined) {
+			set(s, value);
+		} else {
+			sources.set(key, this.#source(value));
+		}
 
-			if (DEV) {
-				tag(s, `SvelteMap get(${label(key)})`);
-			}
+		var items = get(this.#items);
 
-			sources.set(key, s);
-			set(this.#size, super.size);
-			increment(version);
-		} else if (prev_res !== value) {
-			increment(s);
-
-			// if not every reaction of s is a reaction of version we need to also include version
-			var v_reactions = version.reactions === null ? null : new Set(version.reactions);
-			var needs_version_increase =
-				v_reactions === null ||
-				!s.reactions?.every((r) =>
-					/** @type {NonNullable<typeof v_reactions>} */ (v_reactions).has(r)
-				);
-			if (needs_version_increase) {
-				increment(version);
-			}
+		if (!items.has(key)) {
+			const clone = new Map(items);
+			clone.set(key, value);
+
+			set(this.#items, clone);
 		}
 
-		return res;
+		return this;
 	}
 
 	/** @param {K} key */
 	delete(key) {
+		var items = get(this.#items);
+		var has = items.has(key);
 		var sources = this.#sources;
 		var s = sources.get(key);
-		var res = super.delete(key);
 
 		if (s !== undefined) {
 			sources.delete(key);
-			set(s, -1);
+			set(s, /** @type {V} */ (MISSING));
 		}
 
-		if (res) {
-			set(this.#size, super.size);
-			increment(this.#version);
+		if (has) {
+			const clone = new Map(items);
+			clone.delete(key);
+
+			set(this.#items, clone);
 		}
 
-		return res;
+		return has;
 	}
 
 	clear() {
-		if (super.size === 0) {
+		if (get(this.#items).size === 0) {
 			return;
 		}
+
 		// Clear first, so we get nice console.log outputs with $inspect
-		super.clear();
+		set(this.#items, new Map());
+
 		var sources = this.#sources;
-		set(this.#size, 0);
+
 		for (var s of sources.values()) {
-			set(s, -1);
+			set(s, /** @type {V} */ (MISSING));
 		}
-		increment(this.#version);
+
 		sources.clear();
 	}
 
-	#read_all() {
-		get(this.#version);
+	keys() {
+		return get(this.#items).keys();
+	}
 
-		var sources = this.#sources;
-		if (this.#size.v !== sources.size) {
-			for (var key of super.keys()) {
-				if (!sources.has(key)) {
-					var s = this.#source(0);
-					if (DEV) {
-						tag(s, `SvelteMap get(${label(key)})`);
-					}
-
-					sources.set(key, s);
-				}
-			}
-		}
+	*values() {
+		for (const key of get(this.#items).keys()) {
+			const s = this.#sources.get(key);
+			if (s === undefined) continue;
 
-		for ([, s] of this.#sources) {
-			get(s);
+			const value = get(s);
+			if (value !== MISSING) yield value;
 		}
 	}
 
-	keys() {
-		get(this.#version);
-		return super.keys();
-	}
-
-	values() {
-		this.#read_all();
-		return super.values();
-	}
+	*entries() {
+		for (const key of get(this.#items).keys()) {
+			const s = this.#sources.get(key);
+			if (s === undefined) continue;
 
-	entries() {
-		this.#read_all();
-		return super.entries();
+			const value = get(s);
+			if (value !== MISSING) yield [key, value];
+		}
 	}
 
 	[Symbol.iterator]() {
@@ -268,7 +242,6 @@ export class SvelteMap extends Map {
 	}
 
 	get size() {
-		get(this.#size);
-		return super.size;
+		return get(this.#items).size;
 	}
 }