diff --git a/.changelog/6045-feat-directlinespeech-tsup.md b/.changelog/6045-feat-directlinespeech-tsup.md
new file mode 100644
index 0000000000..9998164129
--- /dev/null
+++ b/.changelog/6045-feat-directlinespeech-tsup.md
@@ -0,0 +1,7 @@
+### Changed
+
+- Built `botframework-directlinespeech-sdk` with tsup only, replacing Babel and webpack, in PR [#6045](https://github.com/microsoft/BotFramework-WebChat/pull/6045), by [@OEvgeny](https://github.com/OEvgeny)
+
+### Removed
+
+- 💥 `botframework-directlinespeech-sdk` no longer ships Babel's `lib/` folder: deep imports from `lib/` stop working where `exports` is ignored (webpack 4), in PR [#6045](https://github.com/microsoft/BotFramework-WebChat/pull/6045), by [@OEvgeny](https://github.com/OEvgeny)
diff --git a/docs/BUILD_SCRIPTS.md b/docs/BUILD_SCRIPTS.md
index 98179b950c..7477b4e824 100644
--- a/docs/BUILD_SCRIPTS.md
+++ b/docs/BUILD_SCRIPTS.md
@@ -100,20 +100,19 @@ This section lists verification steps to validate the implementation against the
       -  No instrumentation code (smaller than test builds)
 -  Direct Line Speech SDK
    -  This is tested separately as Direct Line Speech SDK is designed not to live in our monorepo structure
+   -  One `tsup` build produces every output in `dist/`
+      -  `import` loads `botframework-directlinespeech-sdk.mjs`, `require()` loads `botframework-directlinespeech-sdk.js`, with types in `.d.mts` and `.d.ts`
+      -  `<script>` loads `directlinespeech.development.js` or `directlinespeech.production.min.js`, which set `window.DirectLineSpeech`
    -  Development build
       -  Run `npm start` and wait until stabilized
-      -  Verify only `dist/directlinespeech.development.js` is on disk and is about 4 MB in size
+      -  Verify `dist/directlinespeech.development.js` is not minified and is about 1.3 MB in size
    -  Test build
-      -  Set `node_env` to `test`
-      -  Run `npm build` and wait until finished
-         -  Verify `packages/directlinespeech/dist/directlinespeech.production.min.js` is built
-            -  Minified
-            -  Contains instrumentation code but no source maps
+      -  Set `NODE_ENV` to `test`
+      -  Run `npm run build` and wait until finished
+         -  Verify `dist/directlinespeech.production.min.js` is minified and contains instrumentation code (about 580 KB)
       -  Run `npm test -- --ci --coverage false --maxWorkers=4 --no-watch`
-         -  Verify code coverage is collected and correct (`directlinespeech.production.min.js` is about 500 KB)
+         -  Verify code coverage is collected and correct
    -  Production build
-      -  Set `node_env` to `production`
-      -  Run `npm build` and wait until finished
-         -  Verify both `dist/directlinespeech.development.js` and `dist/directlinespeech.production.min.js` are on disk
-            -  `dist/directlinespeech.development.js` is about 3 MB
-            -  `dist/directlinespeech.production.min.js` is about 400 KB
+      -  Set `NODE_ENV` to `production`
+      -  Run `npm run build` and wait until finished
+         -  Verify `dist/directlinespeech.production.min.js` is minified and about 500 KB
diff --git a/package-lock.json b/package-lock.json
index 9bb0d5534e..80570536fd 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11273,6 +11273,7 @@
       "version": "0.6.3",
       "dev": true,
       "license": "MIT",
+      "optional": true,
       "dependencies": {
         "safer-buffer": ">= 2.1.2 < 3.0.0"
       },
@@ -18430,27 +18431,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/source-map-loader": {
-      "version": "5.0.0",
-      "resolved": "https://registry.npmjs.org/source-map-loader/-/source-map-loader-5.0.0.tgz",
-      "integrity": "sha512-k2Dur7CbSLcAH73sBcIkV5xjPV4SzqO1NJ7+XaQl8if3VODDUj3FNchNGpqgJSKbvUfJuhVdv8K2Eu8/TNl2eA==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "iconv-lite": "^0.6.3",
-        "source-map-js": "^1.0.2"
-      },
-      "engines": {
-        "node": ">= 18.12.0"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/webpack"
-      },
-      "peerDependencies": {
-        "webpack": "^5.72.1"
-      }
-    },
     "node_modules/source-map-support": {
       "version": "0.5.13",
       "dev": true,
@@ -20380,13 +20360,6 @@
         "node": ">=10.13.0"
       }
     },
-    "node_modules/webpack-stats-plugin": {
-      "version": "1.1.3",
-      "resolved": "https://registry.npmjs.org/webpack-stats-plugin/-/webpack-stats-plugin-1.1.3.tgz",
-      "integrity": "sha512-yUKYyy+e0iF/w31QdfioRKY+h3jDBRpthexBOWGKda99iu2l/wxYsI/XqdlP5IU58/0KB9CsJZgWNAl+/MPkRw==",
-      "dev": true,
-      "license": "MIT"
-    },
     "node_modules/webpack-virtual-modules": {
       "version": "0.6.2",
       "resolved": "https://registry.npmjs.org/webpack-virtual-modules/-/webpack-virtual-modules-0.6.2.tgz",
@@ -21416,7 +21389,6 @@
       "version": "0.0.0-0",
       "license": "MIT",
       "dependencies": {
-        "@babel/runtime": "7.29.7",
         "abort-controller": "3.0.0",
         "base64-arraybuffer": "1.0.2",
         "core-js": "3.49.0",
@@ -21428,10 +21400,10 @@
         "web-speech-cognitive-services": "8.1.4"
       },
       "devDependencies": {
-        "@babel/cli": "^7.29.7",
         "@babel/core": "^7.29.7",
         "@babel/plugin-transform-runtime": "^7.29.7",
         "@babel/preset-env": "^7.29.7",
+        "@babel/runtime": "7.29.7",
         "@testduet/given-when-then": "^0.1.0",
         "@types/jest": "^29.5.14",
         "@typescript-eslint/eslint-plugin": "^8.60.0",
@@ -21439,7 +21411,6 @@
         "babel-jest": "^29.7.0",
         "babel-plugin-istanbul": "^8.0.0",
         "babel-plugin-transform-inline-environment-variables": "^0.4.4",
-        "cross-env": "^10.1.0",
         "dotenv": "^17.4.2",
         "eslint": "^8.57.1",
         "eslint-plugin-node": "^11.1.0",
@@ -21450,11 +21421,7 @@
         "jest": "^29.7.0",
         "prettier": "^3.8.3",
         "simple-update-in": "^2.2.0",
-        "source-map-loader": "^5.0.0",
-        "tsd": "^0.33.0",
-        "webpack": "^5.107.2",
-        "webpack-cli": "^7.0.3",
-        "webpack-stats-plugin": "^1.1.3"
+        "tsd": "^0.33.0"
       },
       "engines": {
         "node": ">= 10.14.2"
diff --git a/packages/directlinespeech/package.json b/packages/directlinespeech/package.json
index 366ccd297a..3978f5b756 100644
--- a/packages/directlinespeech/package.json
+++ b/packages/directlinespeech/package.json
@@ -4,10 +4,12 @@
   "description": "Direct Line Speech SDK",
   "files": [
     "./dist/**/*",
-    "./lib/**/*",
-    "./src/**/*"
+    "./src/**/*",
+    "!dist/metafile-*.json",
+    "!src/**/*.spec.*",
+    "!src/**/__tests__/**"
   ],
-  "main": "./lib/index.js",
+  "main": "./dist/botframework-directlinespeech-sdk.js",
   "types": "./dist/botframework-directlinespeech-sdk.d.ts",
   "exports": {
     ".": {
@@ -17,7 +19,7 @@
       },
       "require": {
         "types": "./dist/botframework-directlinespeech-sdk.d.ts",
-        "default": "./lib/index.js"
+        "default": "./dist/botframework-directlinespeech-sdk.js"
       }
     }
   },
@@ -35,12 +37,7 @@
     "build:pre": "npm run build:pre:local-dependencies && npm run build:pre:watch",
     "build:pre:local-dependencies": "../../scripts/npm/build-local-dependencies.sh",
     "build:pre:watch": "../../scripts/npm/build-watch.sh",
-    "build:run": "npm run build:run:tsup && npm run build:run:babel && npm run build:run:webpack",
-    "build:run:babel": "cross-env build_tool=babel module_format=commonjs babel src --ignore **/*.spec.js,**/*.test.js,__tests__/**/*.js --out-dir lib --verbose",
-    "build:run:tsup": "tsup",
-    "build:run:webpack": "npm run build:run:webpack:development && npm run build:run:webpack:production",
-    "build:run:webpack:development": "cross-env node_env=development webpack-cli",
-    "build:run:webpack:production": "cross-env node_env=production webpack-cli",
+    "build:run": "tsup",
     "bump": "vg bump prod && vg bump dev && (npm audit fix || exit 0)",
     "eslint": "npm run precommit",
     "postversion": "../../scripts/npm/postversion.sh",
@@ -82,10 +79,10 @@
   },
   "localDependencies": {},
   "devDependencies": {
-    "@babel/cli": "^7.29.7",
     "@babel/core": "^7.29.7",
     "@babel/plugin-transform-runtime": "^7.29.7",
     "@babel/preset-env": "^7.29.7",
+    "@babel/runtime": "7.29.7",
     "@testduet/given-when-then": "^0.1.0",
     "@types/jest": "^29.5.14",
     "@typescript-eslint/eslint-plugin": "^8.60.0",
@@ -93,7 +90,6 @@
     "babel-jest": "^29.7.0",
     "babel-plugin-istanbul": "^8.0.0",
     "babel-plugin-transform-inline-environment-variables": "^0.4.4",
-    "cross-env": "^10.1.0",
     "dotenv": "^17.4.2",
     "eslint": "^8.57.1",
     "eslint-plugin-node": "^11.1.0",
@@ -104,14 +100,9 @@
     "jest": "^29.7.0",
     "prettier": "^3.8.3",
     "simple-update-in": "^2.2.0",
-    "source-map-loader": "^5.0.0",
-    "tsd": "^0.33.0",
-    "webpack": "^5.107.2",
-    "webpack-cli": "^7.0.3",
-    "webpack-stats-plugin": "^1.1.3"
+    "tsd": "^0.33.0"
   },
   "dependencies": {
-    "@babel/runtime": "7.29.7",
     "abort-controller": "3.0.0",
     "base64-arraybuffer": "1.0.2",
     "core-js": "3.49.0",
diff --git a/packages/directlinespeech/src/__tests__/addMetaTag.iife.spec.js b/packages/directlinespeech/src/__tests__/addMetaTag.iife.spec.js
new file mode 100644
index 0000000000..8229801976
--- /dev/null
+++ b/packages/directlinespeech/src/__tests__/addMetaTag.iife.spec.js
@@ -0,0 +1,18 @@
+/** @jest-environment @happy-dom/jest-environment */
+/// <reference types="jest" />
+
+beforeEach(() => {
+  delete window.DirectLineSpeech;
+});
+
+test.each([['directlinespeech.development.js'], ['directlinespeech.production.min.js']])(
+  '%s should set window.DirectLineSpeech with matching buildInfo',
+  filename => {
+    // Loaded as a module (inside a function), not as a classic <script>: only an explicit assignment reaches `window`.
+    jest.requireActual(`../../dist/${filename}`);
+
+    expect(Object.keys(window.DirectLineSpeech).sort()).toEqual(['buildInfo', 'createAdapters']);
+    expect(window.DirectLineSpeech.buildInfo).toHaveProperty('buildTool', 'tsup');
+    expect(window.DirectLineSpeech.buildInfo).toHaveProperty('moduleFormat', 'global');
+  }
+);
diff --git a/packages/directlinespeech/src/bundle.js b/packages/directlinespeech/src/bundle.js
new file mode 100644
index 0000000000..9c69b8e4bf
--- /dev/null
+++ b/packages/directlinespeech/src/bundle.js
@@ -0,0 +1,4 @@
+// Entry of the browser scripts: like the former webpack build (`libraryTarget: 'window'`), assigns `window.DirectLineSpeech`.
+import * as DirectLineSpeech from './index';
+
+window.DirectLineSpeech = DirectLineSpeech;
diff --git a/packages/directlinespeech/tsup.config.ts b/packages/directlinespeech/tsup.config.ts
index 535052d6e9..5c7987de02 100644
--- a/packages/directlinespeech/tsup.config.ts
+++ b/packages/directlinespeech/tsup.config.ts
@@ -21,6 +21,17 @@ const config = applyConfig(config => ({
   noExternal: [...(config.noExternal ?? []), 'event-target-shim']
 }));
 
+// Browser scripts exposing `window.DirectLineSpeech`, with every dependency bundled.
+const iifeConfig = {
+  ...config,
+  dts: false,
+  format: 'iife',
+  outExtension() {
+    return { js: '.js' };
+  },
+  target: [...config.target, 'es2019']
+} satisfies typeof config;
+
 export default defineConfig([
   {
     ...config,
@@ -39,5 +50,33 @@ export default defineConfig([
     },
     format: 'cjs',
     target: [...config.target, 'es2019']
+  },
+  {
+    ...iifeConfig,
+    entry: {
+      'directlinespeech.development': './src/bundle.js'
+    },
+    env: {
+      ...iifeConfig.env,
+      module_format: 'global',
+      node_env: 'development',
+      NODE_ENV: 'development'
+    },
+    // Both browser scripts would write the same metafile-iife.json, keep the production one.
+    metafile: false,
+    minify: false
+  },
+  {
+    ...iifeConfig,
+    entry: {
+      'directlinespeech.production.min': './src/bundle.js'
+    },
+    env: {
+      ...iifeConfig.env,
+      module_format: 'global',
+      node_env: 'production',
+      NODE_ENV: 'production'
+    },
+    minify: true
   }
 ]);
diff --git a/packages/directlinespeech/webpack.config.js b/packages/directlinespeech/webpack.config.js
deleted file mode 100644
index 7446e329c4..0000000000
--- a/packages/directlinespeech/webpack.config.js
+++ /dev/null
@@ -1,48 +0,0 @@
-const { join } = require('path');
-const { StatsWriterPlugin } = require('webpack-stats-plugin');
-
-let config = {
-  entry: './lib/index',
-  mode: 'production',
-  output: {
-    filename: 'directlinespeech.production.min.js',
-    library: 'DirectLineSpeech',
-    libraryTarget: 'window'
-  },
-  plugins: [
-    new StatsWriterPlugin({
-      filename: 'stats.json',
-      transform: (_, opts) => JSON.stringify(opts.compiler.getStats().toJson({ chunkModules: true }), null, 2)
-    })
-  ]
-};
-
-// VSTS always emits uppercase environment variables.
-const node_env = process.env.node_env || process.env.NODE_ENV;
-
-if (node_env !== 'production' && node_env !== 'test') {
-  config = {
-    ...config,
-    devtool: 'eval-source-map',
-    mode: 'development',
-    module: {
-      ...config.module,
-      rules: [
-        ...((config.module || {}).rules || []),
-        {
-          enforce: 'pre',
-          include: [join(__dirname, './lib')],
-          test: /\.js$/,
-          use: ['source-map-loader']
-        }
-      ]
-    },
-    output: {
-      ...config.output,
-      devtoolNamespace: 'botframework-directlinespeech-sdk',
-      filename: 'directlinespeech.development.js'
-    }
-  };
-}
-
-module.exports = config;