diff --git a/packages/ember-application/lib/system/resolver.js b/packages/ember-application/lib/system/resolver.js
index ee8ec96d2aa..f9d57024202 100644
--- a/packages/ember-application/lib/system/resolver.js
+++ b/packages/ember-application/lib/system/resolver.js
@@ -6,8 +6,8 @@ import { dictionary } from 'ember-utils';
 import { get } from 'ember-metal';
 import { assert, info } from 'ember-debug';
 import {
-  String as StringUtils,
   Object as EmberObject,
+  StringUtils,
   Namespace
 } from 'ember-runtime';
 import validateType from '../utils/validate-type';
diff --git a/packages/ember-extension-support/lib/container_debug_adapter.js b/packages/ember-extension-support/lib/container_debug_adapter.js
index b02e0694c53..752b7be9869 100644
--- a/packages/ember-extension-support/lib/container_debug_adapter.js
+++ b/packages/ember-extension-support/lib/container_debug_adapter.js
@@ -2,7 +2,7 @@ import Ember from 'ember-metal'; // Ember as namespace
 import {
   A as emberA,
   typeOf,
-  String as StringUtils,
+  StringUtils,
   Namespace,
   Object as EmberObject
 } from 'ember-runtime';
diff --git a/packages/ember-extension-support/lib/data_adapter.js b/packages/ember-extension-support/lib/data_adapter.js
index c364eb2b759..b25018d9776 100644
--- a/packages/ember-extension-support/lib/data_adapter.js
+++ b/packages/ember-extension-support/lib/data_adapter.js
@@ -1,7 +1,7 @@
 import { getOwner } from 'ember-utils';
 import { get, run, objectAt } from 'ember-metal';
 import {
-  String as StringUtils,
+  StringUtils,
   Namespace,
   Object as EmberObject,
   A as emberA,
diff --git a/packages/ember-glimmer/lib/component-managers/curly.ts b/packages/ember-glimmer/lib/component-managers/curly.ts
index 8e2bebec5fe..23625bd8443 100644
--- a/packages/ember-glimmer/lib/component-managers/curly.ts
+++ b/packages/ember-glimmer/lib/component-managers/curly.ts
@@ -32,7 +32,7 @@ import { DEBUG } from 'ember-env-flags';
 import {
   _instrumentStart, get,
 } from 'ember-metal';
-import { String as StringUtils } from 'ember-runtime';
+import { StringUtils } from 'ember-runtime';
 import {
   assign,
   getOwner,
diff --git a/packages/ember-glimmer/lib/helpers/-class.ts b/packages/ember-glimmer/lib/helpers/-class.ts
index 741532c5ee3..e9fecb147ff 100644
--- a/packages/ember-glimmer/lib/helpers/-class.ts
+++ b/packages/ember-glimmer/lib/helpers/-class.ts
@@ -1,5 +1,5 @@
 import { Arguments, VM } from '@glimmer/runtime';
-import { String as StringUtils } from 'ember-runtime';
+import { StringUtils } from 'ember-runtime';
 import { InternalHelperReference } from '../utils/references';
 
 function classHelper({ positional }: any) {
diff --git a/packages/ember-glimmer/lib/helpers/-normalize-class.ts b/packages/ember-glimmer/lib/helpers/-normalize-class.ts
index 3895f772a4e..bf752fe461c 100644
--- a/packages/ember-glimmer/lib/helpers/-normalize-class.ts
+++ b/packages/ember-glimmer/lib/helpers/-normalize-class.ts
@@ -1,5 +1,5 @@
 import { Arguments, VM } from '@glimmer/runtime';
-import { String as StringUtils } from 'ember-runtime';
+import { StringUtils } from 'ember-runtime';
 import { InternalHelperReference } from '../utils/references';
 
 function normalizeClass({ positional }: any) {
diff --git a/packages/ember-glimmer/lib/helpers/loc.ts b/packages/ember-glimmer/lib/helpers/loc.ts
index 07ec7abfd53..d36401a9081 100644
--- a/packages/ember-glimmer/lib/helpers/loc.ts
+++ b/packages/ember-glimmer/lib/helpers/loc.ts
@@ -3,7 +3,7 @@
 @module ember
 */
 
-import { String as StringUtils } from 'ember-runtime';
+import { StringUtils } from 'ember-runtime';
 import { helper } from '../helper';
 
 /**
diff --git a/packages/ember-glimmer/lib/index.ts b/packages/ember-glimmer/lib/index.ts
index ee4ebf20bb5..459c553091c 100644
--- a/packages/ember-glimmer/lib/index.ts
+++ b/packages/ember-glimmer/lib/index.ts
@@ -273,7 +273,9 @@ export {
   SafeString,
   escapeExpression,
   htmlSafe,
-  isHTMLSafe
+  deprecatedHTMLSafe,
+  isHTMLSafe,
+  deprecatedIsHTMLSafe,
 } from './utils/string';
 export {
   Renderer,
diff --git a/packages/ember-glimmer/lib/utils/bindings.ts b/packages/ember-glimmer/lib/utils/bindings.ts
index 15c64b4823d..de84661de79 100644
--- a/packages/ember-glimmer/lib/utils/bindings.ts
+++ b/packages/ember-glimmer/lib/utils/bindings.ts
@@ -17,7 +17,7 @@ import {
 import { Core, Ops } from '@glimmer/wire-format';
 import { assert } from 'ember-debug';
 import { get } from 'ember-metal';
-import { String as StringUtils } from 'ember-runtime';
+import { StringUtils } from 'ember-runtime';
 import { ROOT_REF } from '../component';
 import { Component } from './curly-component-state-bucket';
 import { referenceFromParts } from './references';
diff --git a/packages/ember-glimmer/lib/utils/string.ts b/packages/ember-glimmer/lib/utils/string.ts
index 31e28cc0b4d..aa37e12540a 100644
--- a/packages/ember-glimmer/lib/utils/string.ts
+++ b/packages/ember-glimmer/lib/utils/string.ts
@@ -2,6 +2,8 @@
 @module @ember/string
 */
 
+import { deprecate } from 'ember-debug';
+
 export class SafeString {
   public string: string;
 
@@ -72,6 +74,7 @@ export function escapeExpression(string: any): string {
   @static
   @return {Handlebars.SafeString} A string that will not be HTML escaped by Handlebars.
   @public
+  @deprecated
 */
 export function htmlSafe(str: string) {
   if (str === null || str === undefined) {
@@ -82,6 +85,19 @@ export function htmlSafe(str: string) {
   return new SafeString(str);
 }
 
+export function deprecatedHTMLSafe(str : string) {
+  deprecate(
+    'Ember.String namespace is deprecated. Please, import `htmlSafe` from `ember/template`.',
+    false,
+    {
+      id: 'ember-glimmer.ember-string-html-safe',
+      until: '3.5.0',
+      url: ''
+    }
+  );
+  return htmlSafe(str);
+}
+
 /**
   Detects if a string was decorated using `htmlSafe`.
 
@@ -100,7 +116,21 @@ export function htmlSafe(str: string) {
   @static
   @return {Boolean} `true` if the string was decorated with `htmlSafe`, `false` otherwise.
   @public
+  @deprecated
 */
 export function isHTMLSafe(str: any | null | undefined): str is SafeString {
   return str !== null && typeof str === 'object' && typeof str.toHTML === 'function';
 }
+
+export function deprecatedIsHTMLSafe(str: string | SafeString): str is SafeString {
+  deprecate(
+    'Ember.String namespace is deprecated. Please, import `isHTMLSafe` from `ember/template`.',
+    false,
+    {
+      id: 'ember-glimmer.ember-string-is-html-safe',
+      until: '3.5.0',
+      url: ''
+    }
+  );
+  return isHTMLSafe(str);
+}
diff --git a/packages/ember-glimmer/tests/utils/helpers.js b/packages/ember-glimmer/tests/utils/helpers.js
index 5176c6f49d3..34b8d2bc72a 100644
--- a/packages/ember-glimmer/tests/utils/helpers.js
+++ b/packages/ember-glimmer/tests/utils/helpers.js
@@ -12,7 +12,9 @@ export {
   InteractiveRender,
   InertRenderer,
   htmlSafe,
+  deprecatedHTMLSafe,
   SafeString,
   DOMChanges,
-  isHTMLSafe
+  isHTMLSafe,
+  deprecatedIsHTMLSafe
 } from 'ember-glimmer';
diff --git a/packages/ember-glimmer/tests/utils/string-test.js b/packages/ember-glimmer/tests/utils/string-test.js
index c3fe64b1934..7a7513b327e 100644
--- a/packages/ember-glimmer/tests/utils/string-test.js
+++ b/packages/ember-glimmer/tests/utils/string-test.js
@@ -1,8 +1,19 @@
-import { SafeString, htmlSafe, isHTMLSafe } from './helpers';
+import {
+  SafeString,
+  htmlSafe,
+  deprecatedHTMLSafe,
+  isHTMLSafe,
+  deprecatedIsHTMLSafe
+} from './helpers';
 import { TestCase } from './abstract-test-case';
 import { moduleFor } from './test-case';
 
 moduleFor('SafeString', class extends TestCase {
+  ['@test deprecated version is deprecated']() {
+    expectDeprecation(/ember\/template/);
+    deprecatedHTMLSafe("Hello");
+  }
+
   ['@test htmlSafe should return an instance of SafeString']() {
     let safeString = htmlSafe('you need to be more <b>bold</b>');
 
@@ -25,6 +36,11 @@ moduleFor('SafeString', class extends TestCase {
 });
 
 moduleFor('SafeString isHTMLSafe', class extends TestCase {
+  ['@test deprecated version is deprecated']() {
+    expectDeprecation(/ember\/template/);
+    deprecatedIsHTMLSafe("Hello");
+  }
+
   ['@test isHTMLSafe should detect SafeString']() {
     let safeString = htmlSafe('<em>Emphasize</em> the important things.');
 
diff --git a/packages/ember-routing/lib/system/route.js b/packages/ember-routing/lib/system/route.js
index cb1d7224bd1..b981db54e6e 100644
--- a/packages/ember-routing/lib/system/route.js
+++ b/packages/ember-routing/lib/system/route.js
@@ -13,7 +13,7 @@ import { DEBUG } from 'ember-env-flags';
 import {
   typeOf,
   copy,
-  String as StringUtils,
+  StringUtils,
   Object as EmberObject,
   A as emberA,
   Evented,
diff --git a/packages/ember-runtime/lib/ext/string.js b/packages/ember-runtime/lib/ext/string.js
index dc05fa46ee7..1530b45ba2f 100644
--- a/packages/ember-runtime/lib/ext/string.js
+++ b/packages/ember-runtime/lib/ext/string.js
@@ -3,6 +3,7 @@
 */
 
 import { ENV } from 'ember-environment';
+import { deprecate } from 'ember-debug';
 import {
   w,
   loc,
@@ -16,7 +17,24 @@ import {
 
 const StringPrototype = String.prototype;
 
+function deprecateEmberStringPrototypeExtension(name, fn, opts = {}) {
+  return function (...args) {
+    deprecate(
+      opts.message || `String prototype extensions are deprecated. Please, use ${name} from '@ember/string' instead.`,
+      false,
+      opts.options || {
+        id: 'ember-string.prototype_extensions',
+        until: '3.5.0',
+        url: 'https://emberjs.com/deprecations/v2.x/#toc_ember-string-prototype-extensions'
+      }
+    );
+
+    return fn(this, ...args);
+  };
+}
+
 if (ENV.EXTEND_PROTOTYPES.String) {
+
   /**
     See [String.w](/api/ember/release/classes/String/methods/w?anchor=w).
 
@@ -29,9 +47,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return w(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('w', w)
   });
 
   /**
@@ -46,9 +62,9 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function(...args) {
-      return loc(this, args);
-    }
+    value: deprecateEmberStringPrototypeExtension('loc', loc, {
+      message: '`loc` is deprecated. Please, use an i18n addon instead. See https://emberobserver.com/categories/internationalization for a list of them.',
+    })
   });
 
   /**
@@ -63,9 +79,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return camelize(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('camelize', camelize)
   });
 
   /**
@@ -80,9 +94,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return decamelize(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('decamelize', decamelize)
   });
 
   /**
@@ -97,9 +109,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return dasherize(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('dasherize', dasherize)
   });
 
   /**
@@ -114,9 +124,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return underscore(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('underscore', underscore)
   });
 
   /**
@@ -131,9 +139,7 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return classify(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('classify', classify)
   });
 
   /**
@@ -148,8 +154,6 @@ if (ENV.EXTEND_PROTOTYPES.String) {
     configurable: true,
     enumerable: false,
     writeable: true,
-    value: function() {
-      return capitalize(this);
-    }
+    value: deprecateEmberStringPrototypeExtension('capitalize', capitalize)
   });
 }
diff --git a/packages/ember-runtime/lib/index.d.ts b/packages/ember-runtime/lib/index.d.ts
index bd8cc8ebd5b..6b1d355b996 100644
--- a/packages/ember-runtime/lib/index.d.ts
+++ b/packages/ember-runtime/lib/index.d.ts
@@ -18,6 +18,20 @@ export const String: {
   loc(s: string, ...args: string[]): string;
 };
 
+export const StringUtils: {
+  fmt(s: string, ...args: any[]): string,
+  loc(s: string, ...args: any[]): string,
+  w(s: string): string[],
+  decamelize(s: string): string,
+  dasherize(s: string): string,
+  camelize(s: string): string,
+  classify(s: string): string,
+  underscore(s: string): string,
+  capitalize(s: string): string
+}
+
+export function objectAt(arr: any, i: number): any;
+
 export function isEmberArray(arr: any): boolean;
 
 export function _contentFor(proxy: any): any;
diff --git a/packages/ember-runtime/lib/index.js b/packages/ember-runtime/lib/index.js
index ab57fb0d994..6480c2cbd25 100644
--- a/packages/ember-runtime/lib/index.js
+++ b/packages/ember-runtime/lib/index.js
@@ -1,5 +1,5 @@
 export { default as Object, FrameworkObject } from './system/object';
-export { default as String } from './system/string';
+export { default as String, StringUtils } from './system/string';
 export {
   default as RegistryProxyMixin,
 } from './mixins/registry_proxy';
diff --git a/packages/ember-runtime/lib/system/string.js b/packages/ember-runtime/lib/system/string.js
index fc647aa08cd..a7f0d2acaef 100644
--- a/packages/ember-runtime/lib/system/string.js
+++ b/packages/ember-runtime/lib/system/string.js
@@ -1,6 +1,7 @@
 /**
 @module @ember/string
 */
+import { deprecate } from 'ember-debug';
 import { Cache } from 'ember-metal';
 import { inspect } from 'ember-utils';
 import { isArray } from '../utils';
@@ -105,6 +106,22 @@ function capitalize(str) {
   return CAPITALIZE_CACHE.get(str);
 }
 
+export function deprecateEmberStringUtil(name, fn, opts = {}) {
+  return function (...args) {
+    deprecate(
+      opts.message || `Ember.String namespace is deprecated. Please, use ${name} from '@ember/string' instead.`,
+      false,
+      opts.options || {
+        id: 'ember-string.namespace',
+        until: '3.5.0',
+        url: 'https://emberjs.com/deprecations/v2.x/#toc_ember-string-namespace'
+      }
+    );
+
+    return fn(...args);
+  };
+}
+
 /**
   Defines string helper methods including string formatting and localization.
   Unless `EmberENV.EXTEND_PROTOTYPES.String` is `false` these methods will also be
@@ -139,8 +156,9 @@ export default {
     @param {Array} formats Optional array of parameters to interpolate into string.
     @return {String} formatted string
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  loc,
+  loc: deprecateEmberStringUtil('loc', loc),
 
   /**
     Splits a string into separate units separated by spaces, eliminating any
@@ -163,8 +181,9 @@ export default {
     @param {String} str The string to split
     @return {Array} array containing the split strings
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  w,
+  w: deprecateEmberStringUtil('w', w),
 
   /**
     Converts a camelized string into all lower case separated by underscores.
@@ -180,8 +199,9 @@ export default {
     @param {String} str The string to decamelize.
     @return {String} the decamelized string.
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  decamelize,
+  decamelize: deprecateEmberStringUtil('decamelize', decamelize),
 
   /**
     Replaces underscores, spaces, or camelCase with dashes.
@@ -198,8 +218,9 @@ export default {
     @param {String} str The string to dasherize.
     @return {String} the dasherized string.
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  dasherize,
+  dasherize: deprecateEmberStringUtil('dasherize', dasherize),
 
   /**
     Returns the lowerCamelCase form of a string.
@@ -217,8 +238,9 @@ export default {
     @param {String} str The string to camelize.
     @return {String} the camelized string.
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  camelize,
+  camelize: deprecateEmberStringUtil('camelize', camelize),
 
   /**
     Returns the UpperCamelCase form of a string.
@@ -235,8 +257,9 @@ export default {
     @param {String} str the string to classify
     @return {String} the classified string
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  classify,
+  classify: deprecateEmberStringUtil('classify', classify),
 
   /**
     More general than decamelize. Returns the lower\_case\_and\_underscored
@@ -254,8 +277,9 @@ export default {
     @param {String} str The string to underscore.
     @return {String} the underscored string.
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  underscore,
+  underscore: deprecateEmberStringUtil('underscore', underscore),
 
   /**
     Returns the Capitalized form of a string
@@ -272,8 +296,9 @@ export default {
     @param {String} str The string to capitalize.
     @return {String} The capitalized string.
     @public
+    @deprecated Use @ember/string addon instead.
   */
-  capitalize
+  capitalize: deprecateEmberStringUtil('capitalize', capitalize)
 };
 
 export {
@@ -286,3 +311,14 @@ export {
   underscore,
   capitalize
 };
+
+export const StringUtils = {
+  loc,
+  w,
+  decamelize,
+  dasherize,
+  camelize,
+  classify,
+  underscore,
+  capitalize
+};
diff --git a/packages/ember-runtime/tests/system/string/camelize_test.js b/packages/ember-runtime/tests/system/string/camelize_test.js
index 433b9378aa6..a37992f72c2 100644
--- a/packages/ember-runtime/tests/system/string/camelize_test.js
+++ b/packages/ember-runtime/tests/system/string/camelize_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { camelize } from '../../../system/string';
+import { camelize, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.camelize');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.camelize is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.camelize('hello world');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(camelize(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.camelize(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/capitalize_test.js b/packages/ember-runtime/tests/system/string/capitalize_test.js
index 07064a16a17..cc872ede19b 100644
--- a/packages/ember-runtime/tests/system/string/capitalize_test.js
+++ b/packages/ember-runtime/tests/system/string/capitalize_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { capitalize } from '../../../system/string';
+import { capitalize, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.capitalize');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.capitalize is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.capitalize('hello world');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(capitalize(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.capitalize(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/classify_test.js b/packages/ember-runtime/tests/system/string/classify_test.js
index 83c4d1b97d8..979873992fb 100644
--- a/packages/ember-runtime/tests/system/string/classify_test.js
+++ b/packages/ember-runtime/tests/system/string/classify_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { classify } from '../../../system/string';
+import { classify, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.classify');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.classify is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.classify('hello world');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(classify(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.classify(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/dasherize_test.js b/packages/ember-runtime/tests/system/string/dasherize_test.js
index a2ed66bfe51..c05894df530 100644
--- a/packages/ember-runtime/tests/system/string/dasherize_test.js
+++ b/packages/ember-runtime/tests/system/string/dasherize_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { dasherize } from '../../../system/string';
+import { dasherize, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.dasherize');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.dasherize is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.dasherize('HelloWorld');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(dasherize(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.dasherize(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/decamelize_test.js b/packages/ember-runtime/tests/system/string/decamelize_test.js
index f635e18825d..677b79d157e 100644
--- a/packages/ember-runtime/tests/system/string/decamelize_test.js
+++ b/packages/ember-runtime/tests/system/string/decamelize_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { decamelize } from '../../../system/string';
+import { decamelize, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.decamelize');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.decamelize is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.decamelize('HelloWorld');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(decamelize(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.decamelize(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/loc_test.js b/packages/ember-runtime/tests/system/string/loc_test.js
index 1d9926a22e2..21739c41397 100644
--- a/packages/ember-runtime/tests/system/string/loc_test.js
+++ b/packages/ember-runtime/tests/system/string/loc_test.js
@@ -1,8 +1,8 @@
+import Ember from 'ember-metal';
 import { ENV } from 'ember-environment';
 import { loc } from '../../../system/string';
 import { setStrings, getStrings } from '../../../string_registry';
 
-
 let oldString;
 
 QUnit.module('EmberStringUtils.loc', {
@@ -27,10 +27,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.loc is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  Ember.String.loc('_Hello World', []);
+});
+
 function test(given, args, expected, description) {
   QUnit.test(description, function(assert) {
     assert.equal(loc(given, args), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/`loc` is deprecated/);
       assert.equal(given.loc(...args), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/underscore_test.js b/packages/ember-runtime/tests/system/string/underscore_test.js
index 52ac5acc806..61e86a099b4 100644
--- a/packages/ember-runtime/tests/system/string/underscore_test.js
+++ b/packages/ember-runtime/tests/system/string/underscore_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { underscore } from '../../../system/string';
+import { underscore, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.underscore');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.underscore is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.underscore('hello world');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(underscore(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.underscore(), expected);
     }
   });
diff --git a/packages/ember-runtime/tests/system/string/w_test.js b/packages/ember-runtime/tests/system/string/w_test.js
index d42194851fb..275a5ecd426 100644
--- a/packages/ember-runtime/tests/system/string/w_test.js
+++ b/packages/ember-runtime/tests/system/string/w_test.js
@@ -1,5 +1,5 @@
 import { ENV } from 'ember-environment';
-import { w } from '../../../system/string';
+import { w, default as EmberString } from '../../../system/string';
 
 QUnit.module('EmberStringUtils.w');
 
@@ -9,10 +9,16 @@ if (!ENV.EXTEND_PROTOTYPES.String) {
   });
 }
 
+QUnit.test('Ember.String.w is deprecated', function() {
+  expectDeprecation(/Ember.String namespace is deprecated/);
+  EmberString.w('Hello World');
+});
+
 function test(given, expected, description) {
   QUnit.test(description, function(assert) {
     assert.deepEqual(w(given), expected);
     if (ENV.EXTEND_PROTOTYPES.String) {
+      expectDeprecation(/@ember\/string/);
       assert.deepEqual(given.w(), expected);
     }
   });
diff --git a/packages/ember/lib/index.js b/packages/ember/lib/index.js
index 78d87cd073a..20cf774cef0 100644
--- a/packages/ember/lib/index.js
+++ b/packages/ember/lib/index.js
@@ -424,9 +424,11 @@ import {
   TextField,
   TextArea,
   LinkComponent,
+  deprecatedHTMLSafe,
   htmlSafe,
   template,
   escapeExpression,
+  deprecatedIsHTMLSafe,
   isHTMLSafe,
   getTemplates,
   setTemplates
@@ -442,6 +444,15 @@ Ember.LinkComponent = LinkComponent;
 
 if (ENV.EXTEND_PROTOTYPES.String) {
   String.prototype.htmlSafe = function() {
+    deprecate(
+      `Extending String prototype is deprecated. Please, use htmlSafe from 'ember/template'.`,
+      false,
+      {
+        id: 'ember-runtime.string-prototype-extension',
+        until: '3.5.0',
+        url: ''
+      }
+    );
     return htmlSafe(this);
   };
 }
@@ -452,9 +463,9 @@ let EmberHandleBarsUtils = EmberHandlebars.Utils = EmberHandlebars.Utils || {};
 
 EmberHTMLBars.template = EmberHandlebars.template = template;
 EmberHandleBarsUtils.escapeExpression = escapeExpression;
-EmberString.htmlSafe = htmlSafe;
+EmberString.htmlSafe = deprecatedHTMLSafe;
 
-EmberString.isHTMLSafe = isHTMLSafe;
+EmberString.isHTMLSafe = deprecatedIsHTMLSafe;
 
 /**
   Global hash of shared templates. This will automatically be populated
@@ -473,6 +484,19 @@ Object.defineProperty(Ember, 'TEMPLATES', {
   enumerable: false
 });
 
+/**
+ Global for safe usage of methods coming from module 'ember/template'.
+
+ @property Template
+ @for Ember
+ @type Object
+ @private
+ */
+Ember._Template = {
+  htmlSafe,
+  isHTMLSafe
+};
+
 import VERSION from './version';
 export { VERSION };
 
diff --git a/packages/ember/tests/reexports_test.js b/packages/ember/tests/reexports_test.js
index eadf0fec202..79068e6c560 100644
--- a/packages/ember/tests/reexports_test.js
+++ b/packages/ember/tests/reexports_test.js
@@ -130,7 +130,9 @@ let allExports =[
   ['TEMPLATES',     'ember-glimmer', { get: 'getTemplates', set: 'setTemplates' }],
   ['Handlebars.template', 'ember-glimmer', 'template'],
   ['Handlebars.Utils.escapeExpression', 'ember-glimmer', 'escapeExpression'],
-  ['String.htmlSafe', 'ember-glimmer', 'htmlSafe'],
+  ['String.htmlSafe', 'ember-glimmer', 'deprecatedHTMLSafe'],
+  ['_Template.htmlSafe', 'ember-glimmer', 'htmlSafe'],
+  ['_Template.isHTMLSafe', 'ember-glimmer', 'isHTMLSafe'],
 
   // ember-runtime
   ['_RegistryProxyMixin', 'ember-runtime', 'RegistryProxyMixin'],
@@ -214,7 +216,7 @@ allExports.forEach(reexport => {
 });
 
 QUnit.test('Ember.String.isHTMLSafe exports correctly', function(assert) {
-  confirmExport(Ember, assert, 'String.isHTMLSafe', 'ember-glimmer', 'isHTMLSafe');
+  confirmExport(Ember, assert, 'String.isHTMLSafe', 'ember-glimmer', 'deprecatedIsHTMLSafe');
 });
 
 if (DEBUG) {
diff --git a/packages/ember/tests/routing/query_params_test.js b/packages/ember/tests/routing/query_params_test.js
index 50f83fbfcc7..1e391058a2d 100644
--- a/packages/ember/tests/routing/query_params_test.js
+++ b/packages/ember/tests/routing/query_params_test.js
@@ -3,7 +3,7 @@ import {
   RSVP,
   Object as EmberObject,
   A as emberA,
-  String as StringUtils
+  StringUtils
 } from 'ember-runtime';
 import {
   run,
diff --git a/packages/ember/tests/routing/router_service_test/urlFor_test.js b/packages/ember/tests/routing/router_service_test/urlFor_test.js
index 61fca5e3766..27d59e0a4f1 100644
--- a/packages/ember/tests/routing/router_service_test/urlFor_test.js
+++ b/packages/ember/tests/routing/router_service_test/urlFor_test.js
@@ -1,6 +1,6 @@
 import {
   Controller,
-  String
+  StringUtils
 } from 'ember-runtime';
 import { Route } from 'ember-routing';
 import {
@@ -14,7 +14,7 @@ import {
 import { EMBER_ROUTING_ROUTER_SERVICE } from 'ember/features';
 
 function setupController(app, name) {
-  let controllerName = `${String.capitalize(name)}Controller`;
+  let controllerName = `${StringUtils.capitalize(name)}Controller`;
 
   Object.defineProperty(app, controllerName, {
     get() {