diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 31ef9110df..371a823225 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -1030,9 +1030,11 @@ declare module 'svelte/compiler' {
 		/**
 		 * If `true`, tells the compiler to generate a custom element constructor instead of a regular Svelte component.
 		 *
+		 * You can also pass a function that receives `{ filename }` and returns a boolean.
+		 *
 		 * @default false
 		 */
-		customElement?: boolean;
+		customElement?: boolean | ((options: { filename: string }) => boolean);
 		/**
 		 * If `true`, getters and setters will be created for the component's props. If `false`, they will only be created for readonly exported values (i.e. those declared with `const`, `class` and `function`). If compiling with `customElement: true` this option defaults to `true`.
 		 *
@@ -1058,8 +1060,10 @@ declare module 'svelte/compiler' {
 		 * - `'injected'`: styles will be included in the `head` when using `render(...)`, and injected into the document (if not already present) when the component mounts. For components compiled as custom elements, styles are injected to the shadow root.
 		 * - `'external'`: the CSS will only be returned in the `css` field of the compilation result. Most Svelte bundler plugins will set this to `'external'` and use the CSS that is statically generated for better performance, as it will result in smaller JavaScript bundles and the output can be served as cacheable `.css` files.
 		 * This is always `'injected'` when compiling with `customElement` mode.
+		 *
+		 * You can also pass a function that receives `{ filename }` and returns either `'injected'` or `'external'`.
 		 */
-		css?: 'injected' | 'external';
+		css?: 'injected' | 'external' | ((options: { filename: string }) => 'injected' | 'external');
 		/**
 		 * A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS.
 		 * It defaults to returning `svelte-${hash(filename ?? css)}`.
@@ -1099,7 +1103,7 @@ declare module 'svelte/compiler' {
 		 * which is likely not what you want. If you're using Vite, consider using [dynamicCompileOptions](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/config.md#dynamiccompileoptions) instead.
 		 * @default undefined
 		 */
-		runes?: boolean | undefined;
+		runes?: boolean | undefined | ((options: { filename: string }) => boolean | undefined);
 		/**
 		 *  If `true`, exposes the Svelte major version in the browser by adding it to a `Set` stored in the global `window.__svelte.v`.
 		 *
@@ -3006,9 +3010,11 @@ declare module 'svelte/types/compiler/interfaces' {
 		/**
 		 * If `true`, tells the compiler to generate a custom element constructor instead of a regular Svelte component.
 		 *
+		 * You can also pass a function that receives `{ filename }` and returns a boolean.
+		 *
 		 * @default false
 		 */
-		customElement?: boolean;
+		customElement?: boolean | ((options: { filename: string }) => boolean);
 		/**
 		 * If `true`, getters and setters will be created for the component's props. If `false`, they will only be created for readonly exported values (i.e. those declared with `const`, `class` and `function`). If compiling with `customElement: true` this option defaults to `true`.
 		 *
@@ -3034,8 +3040,10 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * - `'injected'`: styles will be included in the `head` when using `render(...)`, and injected into the document (if not already present) when the component mounts. For components compiled as custom elements, styles are injected to the shadow root.
 		 * - `'external'`: the CSS will only be returned in the `css` field of the compilation result. Most Svelte bundler plugins will set this to `'external'` and use the CSS that is statically generated for better performance, as it will result in smaller JavaScript bundles and the output can be served as cacheable `.css` files.
 		 * This is always `'injected'` when compiling with `customElement` mode.
+		 *
+		 * You can also pass a function that receives `{ filename }` and returns either `'injected'` or `'external'`.
 		 */
-		css?: 'injected' | 'external';
+		css?: 'injected' | 'external' | ((options: { filename: string }) => 'injected' | 'external');
 		/**
 		 * A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS.
 		 * It defaults to returning `svelte-${hash(filename ?? css)}`.
@@ -3075,7 +3083,7 @@ declare module 'svelte/types/compiler/interfaces' {
 		 * which is likely not what you want. If you're using Vite, consider using [dynamicCompileOptions](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/config.md#dynamiccompileoptions) instead.
 		 * @default undefined
 		 */
-		runes?: boolean | undefined;
+		runes?: boolean | undefined | ((options: { filename: string }) => boolean | undefined);
 		/**
 		 *  If `true`, exposes the Svelte major version in the browser by adding it to a `Set` stored in the global `window.__svelte.v`.
 		 *