diff --git a/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/kibana.json b/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/kibana.json
new file mode 100644
index 00000000000000..10602d2e7981a7
--- /dev/null
+++ b/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/kibana.json
@@ -0,0 +1,4 @@
+{
+  "id": "baz",
+  "ui": true
+}
diff --git a/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/public/index.ts b/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/public/index.ts
new file mode 100644
index 00000000000000..7313de07be04cf
--- /dev/null
+++ b/packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack/baz/public/index.ts
@@ -0,0 +1,21 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+// eslint-disable-next-line no-console
+console.log('plugin in an x-pack dir');
diff --git a/packages/kbn-optimizer/src/common/bundle.test.ts b/packages/kbn-optimizer/src/common/bundle.test.ts
index 6197a084858548..b8f9b94379f200 100644
--- a/packages/kbn-optimizer/src/common/bundle.test.ts
+++ b/packages/kbn-optimizer/src/common/bundle.test.ts
@@ -48,6 +48,7 @@ it('creates cache keys', () => {
         "/foo/bar/c": 789,
       },
       "spec": Object {
+        "banner": undefined,
         "contextDir": "/foo/bar",
         "id": "bar",
         "manifestPath": undefined,
@@ -80,6 +81,7 @@ it('parses bundles from JSON specs', () => {
   expect(bundles).toMatchInlineSnapshot(`
     Array [
       Bundle {
+        "banner": undefined,
         "cache": BundleCache {
           "path": "/foo/bar/target/.kbn-optimizer-cache",
           "state": undefined,
diff --git a/packages/kbn-optimizer/src/common/bundle.ts b/packages/kbn-optimizer/src/common/bundle.ts
index a354da7a21521f..25b37ace09a8fb 100644
--- a/packages/kbn-optimizer/src/common/bundle.ts
+++ b/packages/kbn-optimizer/src/common/bundle.ts
@@ -43,6 +43,8 @@ export interface BundleSpec {
   readonly sourceRoot: string;
   /** Absolute path to the directory where output should be written */
   readonly outputDir: string;
+  /** Banner that should be written to all bundle JS files */
+  readonly banner?: string;
   /** Absolute path to a kibana.json manifest file, if omitted we assume there are not dependenices */
   readonly manifestPath?: string;
 }
@@ -64,6 +66,8 @@ export class Bundle {
   public readonly sourceRoot: BundleSpec['sourceRoot'];
   /** Absolute path to the output directory for this bundle */
   public readonly outputDir: BundleSpec['outputDir'];
+  /** Banner that should be written to all bundle JS files */
+  public readonly banner: BundleSpec['banner'];
   /**
    * Absolute path to a manifest file with "requiredBundles" which will be
    * used to allow bundleRefs from this bundle to the exports of another bundle.
@@ -81,6 +85,7 @@ export class Bundle {
     this.sourceRoot = spec.sourceRoot;
     this.outputDir = spec.outputDir;
     this.manifestPath = spec.manifestPath;
+    this.banner = spec.banner;
 
     this.cache = new BundleCache(Path.resolve(this.outputDir, '.kbn-optimizer-cache'));
   }
@@ -112,6 +117,7 @@ export class Bundle {
       sourceRoot: this.sourceRoot,
       outputDir: this.outputDir,
       manifestPath: this.manifestPath,
+      banner: this.banner,
     };
   }
 
@@ -220,6 +226,13 @@ export function parseBundles(json: string) {
           }
         }
 
+        const { banner } = spec;
+        if (banner !== undefined) {
+          if (!(typeof banner === 'string')) {
+            throw new Error('`bundles[]` must have a string `banner` property');
+          }
+        }
+
         return new Bundle({
           type,
           id,
@@ -227,6 +240,7 @@ export function parseBundles(json: string) {
           contextDir,
           sourceRoot,
           outputDir,
+          banner,
           manifestPath,
         });
       }
diff --git a/packages/kbn-optimizer/src/integration_tests/__snapshots__/basic_optimization.test.ts.snap b/packages/kbn-optimizer/src/integration_tests/__snapshots__/basic_optimization.test.ts.snap
index 4fc259d270e941..cebc668a68dc76 100644
--- a/packages/kbn-optimizer/src/integration_tests/__snapshots__/basic_optimization.test.ts.snap
+++ b/packages/kbn-optimizer/src/integration_tests/__snapshots__/basic_optimization.test.ts.snap
@@ -4,6 +4,7 @@ exports[`builds expected bundles, saves bundle counts to metadata: OptimizerConf
 OptimizerConfig {
   "bundles": Array [
     Bundle {
+      "banner": undefined,
       "cache": BundleCache {
         "path": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/plugins/bar/target/public/.kbn-optimizer-cache,
         "state": undefined,
@@ -19,6 +20,7 @@ OptimizerConfig {
       "type": "plugin",
     },
     Bundle {
+      "banner": undefined,
       "cache": BundleCache {
         "path": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/plugins/foo/target/public/.kbn-optimizer-cache,
         "state": undefined,
@@ -33,6 +35,24 @@ OptimizerConfig {
       "sourceRoot": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo,
       "type": "plugin",
     },
+    Bundle {
+      "banner": "/*! Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one or more contributor license agreements.
+ * Licensed under the Elastic License; you may not use this file except in compliance with the Elastic License. */
+",
+      "cache": BundleCache {
+        "path": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/target/public/.kbn-optimizer-cache,
+        "state": undefined,
+      },
+      "contextDir": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz,
+      "id": "baz",
+      "manifestPath": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/kibana.json,
+      "outputDir": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/target/public,
+      "publicDirNames": Array [
+        "public",
+      ],
+      "sourceRoot": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo,
+      "type": "plugin",
+    },
   ],
   "cache": true,
   "dist": false,
@@ -60,6 +80,13 @@ OptimizerConfig {
       "isUiPlugin": false,
       "manifestPath": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/plugins/nested/baz/kibana.json,
     },
+    Object {
+      "directory": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz,
+      "extraPublicDirs": Array [],
+      "id": "baz",
+      "isUiPlugin": true,
+      "manifestPath": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/kibana.json,
+    },
   ],
   "profileWebpack": false,
   "repoRoot": <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo,
@@ -75,4 +102,9 @@ exports[`prepares assets for distribution: 1 async bundle 1`] = `"(window[\\"foo
 
 exports[`prepares assets for distribution: bar bundle 1`] = `"(function(modules){var installedModules={};function __webpack_require__(moduleId){if(installedModules[moduleId]){return installedModules[moduleId].exports}var module=installedModules[moduleId]={i:moduleId,l:false,exports:{}};modules[moduleId].call(module.exports,module,module.exports,__webpack_require__);module.l=true;return module.exports}__webpack_require__.m=modules;__webpack_require__.c=installedModules;__webpack_require__.d=function(exports,name,getter){if(!__webpack_require__.o(exports,name)){Object.defineProperty(exports,name,{enumerable:true,get:getter})}};__webpack_require__.r=function(exports){if(typeof Symbol!==\\"undefined\\"&&Symbol.toStringTag){Object.defineProperty(exports,Symbol.toStringTag,{value:\\"Module\\"})}Object.defineProperty(exports,\\"__esModule\\",{value:true})};__webpack_require__.t=function(value,mode){if(mode&1)value=__webpack_require__(value);if(mode&8)return value;if(mode&4&&typeof value===\\"object\\"&&value&&value.__esModule)return value;var ns=Object.create(null);__webpack_require__.r(ns);Object.defineProperty(ns,\\"default\\",{enumerable:true,value:value});if(mode&2&&typeof value!=\\"string\\")for(var key in value)__webpack_require__.d(ns,key,function(key){return value[key]}.bind(null,key));return ns};__webpack_require__.n=function(module){var getter=module&&module.__esModule?function getDefault(){return module[\\"default\\"]}:function getModuleExports(){return module};__webpack_require__.d(getter,\\"a\\",getter);return getter};__webpack_require__.o=function(object,property){return Object.prototype.hasOwnProperty.call(object,property)};__webpack_require__.p=\\"\\";return __webpack_require__(__webpack_require__.s=5)})([function(module,exports,__webpack_require__){\\"use strict\\";var isOldIE=function isOldIE(){var memo;return function memorize(){if(typeof memo===\\"undefined\\"){memo=Boolean(window&&document&&document.all&&!window.atob)}return memo}}();var getTarget=function getTarget(){var memo={};return function memorize(target){if(typeof memo[target]===\\"undefined\\"){var styleTarget=document.querySelector(target);if(window.HTMLIFrameElement&&styleTarget instanceof window.HTMLIFrameElement){try{styleTarget=styleTarget.contentDocument.head}catch(e){styleTarget=null}}memo[target]=styleTarget}return memo[target]}}();var stylesInDom=[];function getIndexByIdentifier(identifier){var result=-1;for(var i=0;i<stylesInDom.length;i++){if(stylesInDom[i].identifier===identifier){result=i;break}}return result}function modulesToDom(list,options){var idCountMap={};var identifiers=[];for(var i=0;i<list.length;i++){var item=list[i];var id=options.base?item[0]+options.base:item[0];var count=idCountMap[id]||0;var identifier=\\"\\".concat(id,\\" \\").concat(count);idCountMap[id]=count+1;var index=getIndexByIdentifier(identifier);var obj={css:item[1],media:item[2],sourceMap:item[3]};if(index!==-1){stylesInDom[index].references++;stylesInDom[index].updater(obj)}else{stylesInDom.push({identifier:identifier,updater:addStyle(obj,options),references:1})}identifiers.push(identifier)}return identifiers}function insertStyleElement(options){var style=document.createElement(\\"style\\");var attributes=options.attributes||{};if(typeof attributes.nonce===\\"undefined\\"){var nonce=true?__webpack_require__.nc:undefined;if(nonce){attributes.nonce=nonce}}Object.keys(attributes).forEach((function(key){style.setAttribute(key,attributes[key])}));if(typeof options.insert===\\"function\\"){options.insert(style)}else{var target=getTarget(options.insert||\\"head\\");if(!target){throw new Error(\\"Couldn't find a style target. 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sourceMap=obj.sourceMap;if(media){style.setAttribute(\\"media\\",media)}else{style.removeAttribute(\\"media\\")}if(sourceMap&&btoa){css+=\\"\\\\n/*# sourceMappingURL=data:application/json;base64,\\".concat(btoa(unescape(encodeURIComponent(JSON.stringify(sourceMap)))),\\" */\\")}if(style.styleSheet){style.styleSheet.cssText=css}else{while(style.firstChild){style.removeChild(style.firstChild)}style.appendChild(document.createTextNode(css))}}var singleton=null;var singletonCounter=0;function addStyle(obj,options){var style;var update;var remove;if(options.singleton){var styleIndex=singletonCounter++;style=singleton||(singleton=insertStyleElement(options));update=applyToSingletonTag.bind(null,style,styleIndex,false);remove=applyToSingletonTag.bind(null,style,styleIndex,true)}else{style=insertStyleElement(options);update=applyToTag.bind(null,style,options);remove=function remove(){removeStyleElement(style)}}update(obj);return function 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_index=getIndexByIdentifier(_identifier);if(stylesInDom[_index].references===0){stylesInDom[_index].updater();stylesInDom.splice(_index,1)}}lastIdentifiers=newLastIdentifiers}}},function(module,exports,__webpack_require__){\\"use strict\\";module.exports=function(useSourceMap){var list=[];list.toString=function toString(){return this.map((function(item){var content=cssWithMappingToString(item,useSourceMap);if(item[2]){return\\"@media \\".concat(item[2],\\" {\\").concat(content,\\"}\\")}return content})).join(\\"\\")};list.i=function(modules,mediaQuery,dedupe){if(typeof modules===\\"string\\"){modules=[[null,modules,\\"\\"]]}var alreadyImportedModules={};if(dedupe){for(var i=0;i<this.length;i++){var id=this[i][0];if(id!=null){alreadyImportedModules[id]=true}}}for(var _i=0;_i<modules.length;_i++){var item=[].concat(modules[_i]);if(dedupe&&alreadyImportedModules[item[0]]){continue}if(mediaQuery){if(!item[2]){item[2]=mediaQuery}else{item[2]=\\"\\".concat(mediaQuery,\\" and 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__webpack_require__(23)}},function(module,exports,__webpack_require__){var api=__webpack_require__(0);var content=__webpack_require__(18);content=content.__esModule?content.default:content;if(typeof content===\\"string\\"){content=[[module.i,content,\\"\\"]]}var options={};options.insert=\\"head\\";options.singleton=false;var update=api(content,options);var exported=content.locals?content.locals:{};module.exports=exported},function(module,exports,__webpack_require__){var ___CSS_LOADER_API_IMPORT___=__webpack_require__(1);exports=___CSS_LOADER_API_IMPORT___(false);exports.push([module.i,\\"body {\\\\n  color: green; }\\\\n\\",\\"\\"]);module.exports=exports},function(module,exports,__webpack_require__){var api=__webpack_require__(0);var content=__webpack_require__(20);content=content.__esModule?content.default:content;if(typeof content===\\"string\\"){content=[[module.i,content,\\"\\"]]}var options={};options.insert=\\"head\\";options.singleton=false;var update=api(content,options);var exported=content.locals?content.locals:{};module.exports=exported},function(module,exports,__webpack_require__){var ___CSS_LOADER_API_IMPORT___=__webpack_require__(1);exports=___CSS_LOADER_API_IMPORT___(false);exports.push([module.i,\\"body {\\\\n  color: green; }\\\\n\\",\\"\\"]);module.exports=exports},function(module,exports,__webpack_require__){var api=__webpack_require__(0);var content=__webpack_require__(22);content=content.__esModule?content.default:content;if(typeof content===\\"string\\"){content=[[module.i,content,\\"\\"]]}var options={};options.insert=\\"head\\";options.singleton=false;var update=api(content,options);var exported=content.locals?content.locals:{};module.exports=exported},function(module,exports,__webpack_require__){var ___CSS_LOADER_API_IMPORT___=__webpack_require__(1);exports=___CSS_LOADER_API_IMPORT___(false);exports.push([module.i,\\"body {\\\\n  color: green; }\\\\n\\",\\"\\"]);module.exports=exports},function(module,exports,__webpack_require__){var api=__webpack_require__(0);var content=__webpack_require__(24);content=content.__esModule?content.default:content;if(typeof content===\\"string\\"){content=[[module.i,content,\\"\\"]]}var options={};options.insert=\\"head\\";options.singleton=false;var update=api(content,options);var exported=content.locals?content.locals:{};module.exports=exported},function(module,exports,__webpack_require__){var ___CSS_LOADER_API_IMPORT___=__webpack_require__(1);exports=___CSS_LOADER_API_IMPORT___(false);exports.push([module.i,\\"body {\\\\n  color: green; }\\\\n\\",\\"\\"]);module.exports=exports},function(module,__webpack_exports__,__webpack_require__){\\"use strict\\";__webpack_require__.r(__webpack_exports__);var styles=__webpack_require__(7);var public_0=__webpack_require__(16);var public_=__webpack_require__(4);function barLibFn(){return\\"bar\\"}__webpack_require__.d(__webpack_exports__,\\"barLibFn\\",(function(){return barLibFn}));__webpack_require__.d(__webpack_exports__,\\"fooLibFn\\",(function(){return public_[\\"fooLibFn\\"]}))}]);"`;
 
+exports[`prepares assets for distribution: baz bundle 1`] = `
+"/*! Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one or more contributor license agreements.
+ * Licensed under the Elastic License; you may not use this file except in compliance with the Elastic License. */(function(modules){var installedModules={};function __webpack_require__(moduleId){if(installedModules[moduleId]){return installedModules[moduleId].exports}var module=installedModules[moduleId]={i:moduleId,l:false,exports:{}};modules[moduleId].call(module.exports,module,module.exports,__webpack_require__);module.l=true;return module.exports}__webpack_require__.m=modules;__webpack_require__.c=installedModules;__webpack_require__.d=function(exports,name,getter){if(!__webpack_require__.o(exports,name)){Object.defineProperty(exports,name,{enumerable:true,get:getter})}};__webpack_require__.r=function(exports){if(typeof Symbol!==\\"undefined\\"&&Symbol.toStringTag){Object.defineProperty(exports,Symbol.toStringTag,{value:\\"Module\\"})}Object.defineProperty(exports,\\"__esModule\\",{value:true})};__webpack_require__.t=function(value,mode){if(mode&1)value=__webpack_require__(value);if(mode&8)return value;if(mode&4&&typeof value===\\"object\\"&&value&&value.__esModule)return value;var ns=Object.create(null);__webpack_require__.r(ns);Object.defineProperty(ns,\\"default\\",{enumerable:true,value:value});if(mode&2&&typeof value!=\\"string\\")for(var key in value)__webpack_require__.d(ns,key,function(key){return value[key]}.bind(null,key));return ns};__webpack_require__.n=function(module){var getter=module&&module.__esModule?function getDefault(){return module[\\"default\\"]}:function getModuleExports(){return module};__webpack_require__.d(getter,\\"a\\",getter);return getter};__webpack_require__.o=function(object,property){return Object.prototype.hasOwnProperty.call(object,property)};__webpack_require__.p=\\"\\";return __webpack_require__(__webpack_require__.s=0)})([function(module,__webpack_exports__,__webpack_require__){\\"use strict\\";__webpack_require__.r(__webpack_exports__);var _node_modules_val_loader_dist_cjs_js_key_baz_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0__=__webpack_require__(1);var _node_modules_val_loader_dist_cjs_js_key_baz_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0___default=__webpack_require__.n(_node_modules_val_loader_dist_cjs_js_key_baz_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0__);__kbnBundles__.define(\\"plugin/baz/public\\",__webpack_require__,2)},function(module,exports,__webpack_require__){__webpack_require__.p=window.__kbnPublicPath__[\\"baz\\"]},function(module,exports){console.log(\\"plugin in an x-pack dir\\")}]);"
+`;
+
 exports[`prepares assets for distribution: foo bundle 1`] = `"(function(modules){function webpackJsonpCallback(data){var chunkIds=data[0];var moreModules=data[1];var moduleId,chunkId,i=0,resolves=[];for(;i<chunkIds.length;i++){chunkId=chunkIds[i];if(Object.prototype.hasOwnProperty.call(installedChunks,chunkId)&&installedChunks[chunkId]){resolves.push(installedChunks[chunkId][0])}installedChunks[chunkId]=0}for(moduleId in moreModules){if(Object.prototype.hasOwnProperty.call(moreModules,moduleId)){modules[moduleId]=moreModules[moduleId]}}if(parentJsonpFunction)parentJsonpFunction(data);while(resolves.length){resolves.shift()()}}var installedModules={};var installedChunks={0:0};function jsonpScriptSrc(chunkId){return __webpack_require__.p+\\"\\"+({}[chunkId]||chunkId)+\\".plugin.js\\"}function __webpack_require__(moduleId){if(installedModules[moduleId]){return installedModules[moduleId].exports}var module=installedModules[moduleId]={i:moduleId,l:false,exports:{}};modules[moduleId].call(module.exports,module,module.exports,__webpack_require__);module.l=true;return module.exports}__webpack_require__.e=function requireEnsure(chunkId){var promises=[];var installedChunkData=installedChunks[chunkId];if(installedChunkData!==0){if(installedChunkData){promises.push(installedChunkData[2])}else{var promise=new Promise((function(resolve,reject){installedChunkData=installedChunks[chunkId]=[resolve,reject]}));promises.push(installedChunkData[2]=promise);var script=document.createElement(\\"script\\");var onScriptComplete;script.charset=\\"utf-8\\";script.timeout=120;if(__webpack_require__.nc){script.setAttribute(\\"nonce\\",__webpack_require__.nc)}script.src=jsonpScriptSrc(chunkId);var error=new Error;onScriptComplete=function(event){script.onerror=script.onload=null;clearTimeout(timeout);var chunk=installedChunks[chunkId];if(chunk!==0){if(chunk){var errorType=event&&(event.type===\\"load\\"?\\"missing\\":event.type);var realSrc=event&&event.target&&event.target.src;error.message=\\"Loading chunk \\"+chunkId+\\" failed.\\\\n(\\"+errorType+\\": \\"+realSrc+\\")\\";error.name=\\"ChunkLoadError\\";error.type=errorType;error.request=realSrc;chunk[1](error)}installedChunks[chunkId]=undefined}};var timeout=setTimeout((function(){onScriptComplete({type:\\"timeout\\",target:script})}),12e4);script.onerror=script.onload=onScriptComplete;document.head.appendChild(script)}}return Promise.all(promises)};__webpack_require__.m=modules;__webpack_require__.c=installedModules;__webpack_require__.d=function(exports,name,getter){if(!__webpack_require__.o(exports,name)){Object.defineProperty(exports,name,{enumerable:true,get:getter})}};__webpack_require__.r=function(exports){if(typeof Symbol!==\\"undefined\\"&&Symbol.toStringTag){Object.defineProperty(exports,Symbol.toStringTag,{value:\\"Module\\"})}Object.defineProperty(exports,\\"__esModule\\",{value:true})};__webpack_require__.t=function(value,mode){if(mode&1)value=__webpack_require__(value);if(mode&8)return value;if(mode&4&&typeof value===\\"object\\"&&value&&value.__esModule)return value;var ns=Object.create(null);__webpack_require__.r(ns);Object.defineProperty(ns,\\"default\\",{enumerable:true,value:value});if(mode&2&&typeof value!=\\"string\\")for(var key in value)__webpack_require__.d(ns,key,function(key){return value[key]}.bind(null,key));return ns};__webpack_require__.n=function(module){var getter=module&&module.__esModule?function getDefault(){return module[\\"default\\"]}:function getModuleExports(){return module};__webpack_require__.d(getter,\\"a\\",getter);return getter};__webpack_require__.o=function(object,property){return Object.prototype.hasOwnProperty.call(object,property)};__webpack_require__.p=\\"\\";__webpack_require__.oe=function(err){console.error(err);throw err};var jsonpArray=window[\\"foo_bundle_jsonpfunction\\"]=window[\\"foo_bundle_jsonpfunction\\"]||[];var oldJsonpFunction=jsonpArray.push.bind(jsonpArray);jsonpArray.push=webpackJsonpCallback;jsonpArray=jsonpArray.slice();for(var i=0;i<jsonpArray.length;i++)webpackJsonpCallback(jsonpArray[i]);var parentJsonpFunction=oldJsonpFunction;return __webpack_require__(__webpack_require__.s=0)})([function(module,__webpack_exports__,__webpack_require__){\\"use strict\\";__webpack_require__.r(__webpack_exports__);var _node_modules_val_loader_dist_cjs_js_key_foo_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0__=__webpack_require__(1);var _node_modules_val_loader_dist_cjs_js_key_foo_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0___default=__webpack_require__.n(_node_modules_val_loader_dist_cjs_js_key_foo_kbn_ui_shared_deps_public_path_module_creator_js__WEBPACK_IMPORTED_MODULE_0__);__kbnBundles__.define(\\"plugin/foo/public\\",__webpack_require__,2)},function(module,exports,__webpack_require__){__webpack_require__.p=window.__kbnPublicPath__[\\"foo\\"]},function(module,__webpack_exports__,__webpack_require__){\\"use strict\\";__webpack_require__.r(__webpack_exports__);function fooLibFn(){return\\"foo\\"}var ext=\\"TRUE\\";__webpack_require__.d(__webpack_exports__,\\"getFoo\\",(function(){return getFoo}));__webpack_require__.d(__webpack_exports__,\\"fooLibFn\\",(function(){return fooLibFn}));__webpack_require__.d(__webpack_exports__,\\"ext\\",(function(){return ext}));function asyncGeneratorStep(gen,resolve,reject,_next,_throw,key,arg){try{var info=gen[key](arg);var value=info.value}catch(error){reject(error);return}if(info.done){resolve(value)}else{Promise.resolve(value).then(_next,_throw)}}function _asyncToGenerator(fn){return function(){var self=this,args=arguments;return new Promise((function(resolve,reject){var gen=fn.apply(self,args);function _next(value){asyncGeneratorStep(gen,resolve,reject,_next,_throw,\\"next\\",value)}function _throw(err){asyncGeneratorStep(gen,resolve,reject,_next,_throw,\\"throw\\",err)}_next(undefined)}))}}function getFoo(){return _getFoo.apply(this,arguments)}function _getFoo(){_getFoo=_asyncToGenerator(regeneratorRuntime.mark((function _callee(){return regeneratorRuntime.wrap((function _callee$(_context){while(1){switch(_context.prev=_context.next){case 0:_context.next=2;return __webpack_require__.e(1).then(__webpack_require__.bind(null,3));case 2:return _context.abrupt(\\"return\\",_context.sent);case 3:case\\"end\\":return _context.stop()}}}),_callee)})));return _getFoo.apply(this,arguments)}}]);"`;
diff --git a/packages/kbn-optimizer/src/integration_tests/basic_optimization.test.ts b/packages/kbn-optimizer/src/integration_tests/basic_optimization.test.ts
index 4cf14d9e048c8c..3eb8eb83776b8f 100644
--- a/packages/kbn-optimizer/src/integration_tests/basic_optimization.test.ts
+++ b/packages/kbn-optimizer/src/integration_tests/basic_optimization.test.ts
@@ -66,7 +66,7 @@ afterAll(async () => {
 it('builds expected bundles, saves bundle counts to metadata', async () => {
   const config = OptimizerConfig.create({
     repoRoot: MOCK_REPO_DIR,
-    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins')],
+    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins'), Path.resolve(MOCK_REPO_DIR, 'x-pack')],
     maxWorkerCount: 1,
     dist: false,
   });
@@ -100,7 +100,7 @@ it('builds expected bundles, saves bundle counts to metadata', async () => {
       (msg.event?.type === 'bundle cached' || msg.event?.type === 'bundle not cached') &&
       msg.state.phase === 'initializing'
   );
-  assert('produce two bundle cache events while initializing', bundleCacheStates.length === 2);
+  assert('produce three bundle cache events while initializing', bundleCacheStates.length === 3);
 
   const initializedStates = msgs.filter((msg) => msg.state.phase === 'initialized');
   assert('produce at least one initialized event', initializedStates.length >= 1);
@@ -110,17 +110,17 @@ it('builds expected bundles, saves bundle counts to metadata', async () => {
 
   const runningStates = msgs.filter((msg) => msg.state.phase === 'running');
   assert(
-    'produce two or three "running" states',
-    runningStates.length === 2 || runningStates.length === 3
+    'produce three to five "running" states',
+    runningStates.length >= 3 && runningStates.length <= 5
   );
 
   const bundleNotCachedEvents = msgs.filter((msg) => msg.event?.type === 'bundle not cached');
-  assert('produce two "bundle not cached" events', bundleNotCachedEvents.length === 2);
+  assert('produce three "bundle not cached" events', bundleNotCachedEvents.length === 3);
 
   const successStates = msgs.filter((msg) => msg.state.phase === 'success');
   assert(
-    'produce one or two "compiler success" states',
-    successStates.length === 1 || successStates.length === 2
+    'produce one to three "compiler success" states',
+    successStates.length >= 1 && successStates.length <= 3
   );
 
   const otherStates = msgs.filter(
@@ -175,12 +175,26 @@ it('builds expected bundles, saves bundle counts to metadata', async () => {
       <absolute path>/packages/kbn-ui-shared-deps/public_path_module_creator.js,
     ]
   `);
+
+  const baz = config.bundles.find((b) => b.id === 'baz')!;
+  expect(baz).toBeTruthy();
+  baz.cache.refresh();
+  expect(baz.cache.getModuleCount()).toBe(3);
+
+  expect(baz.cache.getReferencedFiles()).toMatchInlineSnapshot(`
+    Array [
+      <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/kibana.json,
+      <absolute path>/packages/kbn-optimizer/src/__fixtures__/__tmp__/mock_repo/x-pack/baz/public/index.ts,
+      <absolute path>/packages/kbn-optimizer/target/worker/entry_point_creator.js,
+      <absolute path>/packages/kbn-ui-shared-deps/public_path_module_creator.js,
+    ]
+  `);
 });
 
 it('uses cache on second run and exist cleanly', async () => {
   const config = OptimizerConfig.create({
     repoRoot: MOCK_REPO_DIR,
-    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins')],
+    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins'), Path.resolve(MOCK_REPO_DIR, 'x-pack')],
     maxWorkerCount: 1,
     dist: false,
   });
@@ -202,6 +216,7 @@ it('uses cache on second run and exist cleanly', async () => {
       "initializing",
       "initializing",
       "initializing",
+      "initializing",
       "initialized",
       "success",
     ]
@@ -211,7 +226,7 @@ it('uses cache on second run and exist cleanly', async () => {
 it('prepares assets for distribution', async () => {
   const config = OptimizerConfig.create({
     repoRoot: MOCK_REPO_DIR,
-    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins')],
+    pluginScanDirs: [Path.resolve(MOCK_REPO_DIR, 'plugins'), Path.resolve(MOCK_REPO_DIR, 'x-pack')],
     maxWorkerCount: 1,
     dist: true,
   });
@@ -224,6 +239,7 @@ it('prepares assets for distribution', async () => {
     '1 async bundle'
   );
   expectFileMatchesSnapshotWithCompression('plugins/bar/target/public/bar.plugin.js', 'bar bundle');
+  expectFileMatchesSnapshotWithCompression('x-pack/baz/target/public/baz.plugin.js', 'baz bundle');
 });
 
 /**
diff --git a/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.test.ts b/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.test.ts
index a70cfc759dd55b..a823f66cf767b8 100644
--- a/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.test.ts
+++ b/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.test.ts
@@ -48,12 +48,20 @@ it('returns a bundle for core and each plugin', () => {
           extraPublicDirs: [],
           manifestPath: '/outside/of/repo/plugins/baz/kibana.json',
         },
+        {
+          directory: '/repo/x-pack/plugins/box',
+          id: 'box',
+          isUiPlugin: true,
+          extraPublicDirs: [],
+          manifestPath: '/repo/x-pack/plugins/box/kibana.json',
+        },
       ],
       '/repo'
     ).map((b) => b.toSpec())
   ).toMatchInlineSnapshot(`
     Array [
       Object {
+        "banner": undefined,
         "contextDir": <absolute path>/plugins/foo,
         "id": "foo",
         "manifestPath": <absolute path>/plugins/foo/kibana.json,
@@ -65,6 +73,7 @@ it('returns a bundle for core and each plugin', () => {
         "type": "plugin",
       },
       Object {
+        "banner": undefined,
         "contextDir": "/outside/of/repo/plugins/baz",
         "id": "baz",
         "manifestPath": "/outside/of/repo/plugins/baz/kibana.json",
@@ -75,6 +84,20 @@ it('returns a bundle for core and each plugin', () => {
         "sourceRoot": <absolute path>,
         "type": "plugin",
       },
+      Object {
+        "banner": "/*! Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one or more contributor license agreements.
+     * Licensed under the Elastic License; you may not use this file except in compliance with the Elastic License. */
+    ",
+        "contextDir": <absolute path>/x-pack/plugins/box,
+        "id": "box",
+        "manifestPath": <absolute path>/x-pack/plugins/box/kibana.json,
+        "outputDir": <absolute path>/x-pack/plugins/box/target/public,
+        "publicDirNames": Array [
+          "public",
+        ],
+        "sourceRoot": <absolute path>,
+        "type": "plugin",
+      },
     ]
   `);
 });
diff --git a/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.ts b/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.ts
index 04ab992addeec1..9350b9464242af 100644
--- a/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.ts
+++ b/packages/kbn-optimizer/src/optimizer/get_plugin_bundles.ts
@@ -24,6 +24,8 @@ import { Bundle } from '../common';
 import { KibanaPlatformPlugin } from './kibana_platform_plugins';
 
 export function getPluginBundles(plugins: KibanaPlatformPlugin[], repoRoot: string) {
+  const xpackDirSlash = Path.resolve(repoRoot, 'x-pack') + Path.sep;
+
   return plugins
     .filter((p) => p.isUiPlugin)
     .map(
@@ -36,6 +38,10 @@ export function getPluginBundles(plugins: KibanaPlatformPlugin[], repoRoot: stri
           contextDir: p.directory,
           outputDir: Path.resolve(p.directory, 'target/public'),
           manifestPath: p.manifestPath,
+          banner: p.directory.startsWith(xpackDirSlash)
+            ? `/*! Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one or more contributor license agreements.\n` +
+              ` * Licensed under the Elastic License; you may not use this file except in compliance with the Elastic License. */\n`
+            : undefined,
         })
     );
 }
diff --git a/packages/kbn-optimizer/src/worker/webpack.config.ts b/packages/kbn-optimizer/src/worker/webpack.config.ts
index 0b110446af944e..34165de9fe7144 100644
--- a/packages/kbn-optimizer/src/worker/webpack.config.ts
+++ b/packages/kbn-optimizer/src/worker/webpack.config.ts
@@ -69,6 +69,7 @@ export function getWebpackConfig(bundle: Bundle, bundleRefs: BundleRefs, worker:
       new CleanWebpackPlugin(),
       new DisallowedSyntaxPlugin(),
       new BundleRefsPlugin(bundle, bundleRefs),
+      ...(bundle.banner ? [new webpack.BannerPlugin({ banner: bundle.banner, raw: true })] : []),
     ],
 
     module: {
diff --git a/src/dev/precommit_hook/casing_check_config.js b/src/dev/precommit_hook/casing_check_config.js
index 6f680557df0768..6c06150ab8dadd 100644
--- a/src/dev/precommit_hook/casing_check_config.js
+++ b/src/dev/precommit_hook/casing_check_config.js
@@ -103,6 +103,7 @@ export const IGNORE_DIRECTORY_GLOBS = [
   'test/functional/fixtures/es_archiver/visualize_source-filters',
   'packages/kbn-pm/src/utils/__fixtures__/*',
   'x-pack/dev-tools',
+  'packages/kbn-optimizer/src/__fixtures__/mock_repo/x-pack',
 ];
 
 /**