diff --git a/.changeset/stupid-baboons-fall.md b/.changeset/stupid-baboons-fall.md
new file mode 100644
index 0000000000..66895ad015
--- /dev/null
+++ b/.changeset/stupid-baboons-fall.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: abort running obsolete async branches
diff --git a/packages/svelte/src/internal/client/dom/blocks/async.js b/packages/svelte/src/internal/client/dom/blocks/async.js
index 43af3d8dd3..fd9d0a2964 100644
--- a/packages/svelte/src/internal/client/dom/blocks/async.js
+++ b/packages/svelte/src/internal/client/dom/blocks/async.js
@@ -49,23 +49,29 @@ export function async(node, blockers = [], expressions = [], fn) {
 		set_hydrate_node(end);
 	}
 
-	flatten(blockers, [], expressions, (values) => {
-		if (was_hydrating) {
-			set_hydrating(true);
-			set_hydrate_node(previous_hydrate_node);
-		}
-
-		try {
-			// get values eagerly to avoid creating blocks if they reject
-			for (const d of values) get(d);
-
-			fn(node, ...values);
-		} finally {
+	flatten(
+		blockers,
+		[],
+		expressions,
+		(values) => {
 			if (was_hydrating) {
-				set_hydrating(false);
+				set_hydrating(true);
+				set_hydrate_node(previous_hydrate_node);
 			}
 
-			decrement_pending();
-		}
-	});
+			try {
+				// get values eagerly to avoid creating blocks if they reject
+				for (const d of values) get(d);
+
+				fn(node, ...values);
+			} finally {
+				if (was_hydrating) {
+					set_hydrating(false);
+				}
+
+				decrement_pending();
+			}
+		},
+		() => decrement_pending()
+	);
 }
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 6aea790c36..134de3a8fc 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -31,8 +31,9 @@ import { aborted } from './effects.js';
  * @param {Array<() => any>} sync
  * @param {Array<() => Promise<any>>} async
  * @param {(values: Value[]) => any} fn
+ * @param {() => void} [on_abort]
  */
-export function flatten(blockers, sync, async, fn) {
+export function flatten(blockers, sync, async, fn, on_abort) {
 	const d = is_runes() ? derived : derived_safe_equal;
 
 	// Filter out already-settled blockers - no need to wait for them
@@ -57,12 +58,14 @@ export function flatten(blockers, sync, async, fn) {
 	function finish(values) {
 		restore();
 
-		try {
-			fn(values);
-		} catch (error) {
-			if ((parent.f & DESTROYED) === 0) {
+		if ((parent.f & DESTROYED) === 0) {
+			try {
+				fn(values);
+			} catch (error) {
 				invoke_error_boundary(error, parent);
 			}
+		} else {
+			on_abort?.();
 		}
 
 		unset_context();
diff --git a/packages/svelte/src/internal/client/reactivity/deriveds.js b/packages/svelte/src/internal/client/reactivity/deriveds.js
index 5af51449ad..01fdd58831 100644
--- a/packages/svelte/src/internal/client/reactivity/deriveds.js
+++ b/packages/svelte/src/internal/client/reactivity/deriveds.js
@@ -239,7 +239,7 @@ export function async_derived(fn, label, location) {
 					recent_async_deriveds.add(signal);
 
 					setTimeout(() => {
-						if (recent_async_deriveds.has(signal)) {
+						if (recent_async_deriveds.has(signal) && (effect.f & DESTROYED) === 0) {
 							w.await_waterfall(/** @type {string} */ (signal.label), location);
 							recent_async_deriveds.delete(signal);
 						}
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 0fad074e6f..e83a49bc60 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -400,13 +400,18 @@ export function deferred_template_effect(fn, sync = [], async = [], blockers = [
 		var decrement_pending = increment_pending();
 	}
 
-	flatten(blockers, sync, async, (values) => {
-		create_effect(EFFECT, () => fn(...values.map(get)));
-
-		if (decrement_pending) {
-			decrement_pending();
+	flatten(
+		blockers,
+		sync,
+		async,
+		(values) => {
+			create_effect(EFFECT, () => fn(...values.map(get)));
+			decrement_pending?.();
+		},
+		() => {
+			decrement_pending?.();
 		}
-	});
+	);
 }
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte
new file mode 100644
index 0000000000..1d9bdfada2
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/Child.svelte
@@ -0,0 +1,6 @@
+<script>
+	let { count } = $props();
+	let double = $derived(count * 2);
+
+	$effect.pre(() => console.log(count, double));
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js
new file mode 100644
index 0000000000..83364706e5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/_config.js
@@ -0,0 +1,27 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs, warnings }) {
+		const [increment, resolve] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, []);
+
+		resolve.click();
+		await tick();
+		assert.deepEqual(logs, [1, 2]);
+
+		// no await waterfall / inert derived warnings
+		assert.deepEqual(warnings, []);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte
new file mode 100644
index 0000000000..fe01ae457e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-obsolete-branch-no-effect-runs/main.svelte
@@ -0,0 +1,31 @@
+<script>
+	import Child from "./Child.svelte";
+	let count = $state(0);
+
+	let deferreds = [];
+
+	function push(v) {
+		return new Promise((resolve, reject) => {
+			deferreds.push({ resolve: () => resolve(v), reject });
+		});
+	}
+</script>
+
+<button onclick={() => count += 1}>increment</button>
+<button onclick={() => deferreds.shift()?.resolve()}>resolve</button>
+
+<svelte:boundary>
+	{#if count % 2 === 0}
+		{@const double = count * 2}
+		<p>true</p>
+		{await push(count)} {double}
+		<Child count={await push(count)} />
+	{:else}
+		<p>false</p>
+		<Child count={await push(count)} />
+	{/if}
+
+	{#snippet pending()}
+		<p>loading...</p>
+	{/snippet}
+</svelte:boundary>