diff --git a/.changeset/smooth-pens-jump.md b/.changeset/smooth-pens-jump.md
new file mode 100644
index 0000000000..79aea8e6e1
--- /dev/null
+++ b/.changeset/smooth-pens-jump.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: avoid O(n²) name scanning in scope `generate` and `unique`
diff --git a/packages/svelte/src/compiler/phases/scope.js b/packages/svelte/src/compiler/phases/scope.js
index 9d563375d7..e3560753b4 100644
--- a/packages/svelte/src/compiler/phases/scope.js
+++ b/packages/svelte/src/compiler/phases/scope.js
@@ -713,8 +713,18 @@ export class Scope {
 		}
 
 		preferred_name = preferred_name.replace(/[^a-zA-Z0-9_$]/g, '_').replace(/^[0-9]/, '_');
-		let name = preferred_name;
-		let n = 1;
+
+		// Use cached counter to skip names already known to be taken (avoids O(n²) scanning)
+		let n = this.root.next_counter(preferred_name);
+		let name;
+
+		if (n === 0) {
+			name = preferred_name;
+			n = 1;
+		} else {
+			name = `${preferred_name}_${n}`;
+			n++;
+		}
 
 		while (
 			this.references.has(name) ||
@@ -725,6 +735,7 @@ export class Scope {
 			name = `${preferred_name}_${n++}`;
 		}
 
+		this.root.set_counter(preferred_name, n);
 		this.references.set(name, []);
 		this.root.conflicts.add(name);
 		return name;
@@ -852,18 +863,49 @@ export class ScopeRoot {
 	/** @type {Set<string>} */
 	conflicts = new Set();
 
+	/**
+	 * Tracks the next suffix counter per name to avoid O(n) rescanning in generate/unique.
+	 * @type {Map<string, number>}
+	 */
+	#name_counters = new Map();
+
+	/**
+	 * @param {string} name
+	 * @returns {number}
+	 */
+	next_counter(name) {
+		return this.#name_counters.get(name) ?? 0;
+	}
+
+	/**
+	 * @param {string} name
+	 * @param {number} value
+	 */
+	set_counter(name, value) {
+		this.#name_counters.set(name, value);
+	}
+
 	/**
 	 * @param {string} preferred_name
 	 */
 	unique(preferred_name) {
 		preferred_name = preferred_name.replace(/[^a-zA-Z0-9_$]/g, '_');
-		let final_name = preferred_name;
-		let n = 1;
+		let n = this.#name_counters.get(preferred_name) ?? 0;
+		let final_name;
+
+		if (n === 0) {
+			final_name = preferred_name;
+			n = 1;
+		} else {
+			final_name = `${preferred_name}_${n}`;
+			n++;
+		}
 
 		while (this.conflicts.has(final_name)) {
 			final_name = `${preferred_name}_${n++}`;
 		}
 
+		this.#name_counters.set(preferred_name, n);
 		this.conflicts.add(final_name);
 		const id = b.id(final_name);
 		return id;