diff --git a/.changeset/chilly-paws-smell.md b/.changeset/chilly-paws-smell.md
new file mode 100644
index 00000000000..a7f3ea20b54
--- /dev/null
+++ b/.changeset/chilly-paws-smell.md
@@ -0,0 +1,5 @@
+---
+"@astrojs/starlight": patch
+---
+
+Ensures `<Tab>` component toggling is stable when smooth scrolling is enabled via custom CSS
diff --git a/packages/starlight/user-components/Tabs.astro b/packages/starlight/user-components/Tabs.astro
index 4234eb0126a..257174e1dbe 100644
--- a/packages/starlight/user-components/Tabs.astro
+++ b/packages/starlight/user-components/Tabs.astro
@@ -224,6 +224,7 @@ if (isSynced) {
 				StarlightTabs.#syncTabs(this, newTab);
 				window.scrollTo({
 					top: window.scrollY + (this.getBoundingClientRect().top - previousTabsOffset),
+					behavior: 'instant',
 				});
 			}
 		}