diff --git a/examples/official-storybook/main.js b/examples/official-storybook/main.ts
similarity index 96%
rename from examples/official-storybook/main.js
rename to examples/official-storybook/main.ts
index 6eea9d783a01..2c249eff765a 100644
--- a/examples/official-storybook/main.js
+++ b/examples/official-storybook/main.ts
@@ -1,3 +1,5 @@
+import type { StorybookConfig } from '@storybook/core/types';
+
 module.exports = {
   stories: [
     // FIXME: Breaks e2e tests './intro.stories.mdx',
@@ -74,4 +76,4 @@ module.exports = {
       extensions: [...(config.resolve.extensions || []), '.ts', '.tsx'],
     },
   }),
-};
+} as StorybookConfig;
diff --git a/lib/core/types/index.ts b/lib/core/types/index.ts
index 2edb41497374..eaaf4f72a67e 100644
--- a/lib/core/types/index.ts
+++ b/lib/core/types/index.ts
@@ -1,8 +1,9 @@
 import type ForkTsCheckerWebpackPlugin from 'fork-ts-checker-webpack-plugin';
 import type LoaderOptions from 'react-docgen-typescript-loader/dist/LoaderOptions';
+import { Configuration } from 'webpack';
 
 /**
- * The interface for Storybook configuration in `main.js` files.
+ * The interface for Storybook configuration in `main.ts` files.
  */
 export interface StorybookConfig {
   /**
@@ -10,7 +11,7 @@ export interface StorybookConfig {
    *
    * @example `['@storybook/addon-essentials']`
    */
-  addons: string[];
+  addons?: string[];
   /**
    * Tells Storybook where to find stories.
    *
@@ -21,12 +22,20 @@ export interface StorybookConfig {
    * Controls how Storybook hanldes TypeScript files.
    */
   typescript?: Partial<TypescriptOptions>;
+  /**
+   * Modify or return a custom Webpack config.
+   */
+  webpackFinal?: (
+    config: Configuration,
+    options: StorybookOptions
+  ) => Configuration | Promise<Configuration>;
 }
 
 /**
  * The internal options object, used by Storybook frameworks and adddons.
  */
 export interface StorybookOptions {
+  configType: 'DEVELOPMENT' | 'PRODUCTION';
   typescriptOptions: TypescriptOptions;
 }
 
@@ -42,8 +51,11 @@ export interface TypescriptOptions {
   check: boolean;
   /**
    * Configures `fork-ts-checker-webpack-plugin`
+   *
+   * @default
+   * @see https://github.com/storybookjs/storybook/blob/next/lib/core/src/server/config/defaults.js#L4-L6
    */
-  checkOptions?: ForkTsCheckerWebpackPlugin['options'];
+  checkOptions: ForkTsCheckerWebpackPlugin['options'];
   /**
    * Sets the type of Docgen when working with React and TypeScript
    *