diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 993a9245467..1bbbf0bc716 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -35,7 +35,7 @@ jobs:
         working-directory: smoke-tests/scenarios
         run: |
           matrix_json=$(pnpm scenario-tester list --require @swc-node/register --files "*-test.ts" --matrix "pnpm run test --filter %s"   )
-          echo "matrix=$matrix_json" >> $GITHUB_OUTPUT        
+          echo "matrix=$matrix_json" >> $GITHUB_OUTPUT
 
   types:
     name: Type Checking (current version)
@@ -105,9 +105,11 @@ jobs:
             ENABLE_OPTIONAL_FEATURES: "true"
           - name: "Extend prototypes"
             EXTEND_PROTOTYPES: "true"
+            RAISE_ON_DEPRECATION: "false"
           - name: "Extend prototypes, with optional features"
             EXTEND_PROTOTYPES: "true"
             ENABLE_OPTIONAL_FEATURES: "true"
+            RAISE_ON_DEPRECATION: "false"
 
     steps:
       - uses: actions/checkout@v3
@@ -120,6 +122,7 @@ jobs:
           OVERRIDE_DEPRECATION_VERSION: ${{ matrix.OVERRIDE_DEPRECATION_VERSION }}
           EXTEND_PROTOTYPES: ${{ matrix.EXTEND_PROTOTYPES }}
           ENABLE_OPTIONAL_FEATURES: ${{ matrix.ENABLE_OPTIONAL_FEATURES }}
+          RAISE_ON_DEPRECATION: ${{ matrix.RAISE_ON_DEPRECATION }}
 
         run: pnpm test
 
diff --git a/bin/run-tests.js b/bin/run-tests.js
index 2192e1502fc..83087ed9583 100755
--- a/bin/run-tests.js
+++ b/bin/run-tests.js
@@ -1,11 +1,11 @@
 /* eslint-disable no-console */
 'use strict';
 
-/* 
+/*
   Test Variants
 
   These are all accepted as environment variables when running `ember test` or
-  as query params when directly invoking the test suite in the browser. 
+  as query params when directly invoking the test suite in the browser.
 */
 const variants = [
   // When true, even deprecations that are not yet at the "enabled" version will
@@ -25,6 +25,9 @@ const variants = [
   // This enables all canary feature flags for unreleased feature within Ember
   // itself.
   'ENABLE_OPTIONAL_FEATURES',
+
+  // Throw on unexpected deprecations. Defaults to true if not set explicitly.
+  'RAISE_ON_DEPRECATION',
 ];
 
 const chalk = require('chalk');
diff --git a/index.html b/index.html
index 373c6d99fbd..c6fad19b48a 100644
--- a/index.html
+++ b/index.html
@@ -32,15 +32,17 @@
         EmberENV.ENABLE_OPTIONAL_FEATURES = true;
       }
 
-      EmberENV['RAISE_ON_DEPRECATION'] = true;
+      EmberENV['RAISE_ON_DEPRECATION'] = QUnit.urlParams.RAISE_ON_DEPRECATION
+        ? QUnit.urlParams.RAISE_ON_DEPRECATION === 'true'
+        : true;
 
       if (QUnit.urlParams.ALL_DEPRECATIONS_ENABLED) {
-          EmberENV['_ALL_DEPRECATIONS_ENABLED'] = true;
-        }
+        EmberENV['_ALL_DEPRECATIONS_ENABLED'] = true;
+      }
 
-        if (QUnit.urlParams.OVERRIDE_DEPRECATION_VERSION) {
-          EmberENV['_OVERRIDE_DEPRECATION_VERSION'] = QUnit.urlParams.OVERRIDE_DEPRECATION_VERSION;
-        }
+      if (QUnit.urlParams.OVERRIDE_DEPRECATION_VERSION) {
+        EmberENV['_OVERRIDE_DEPRECATION_VERSION'] = QUnit.urlParams.OVERRIDE_DEPRECATION_VERSION;
+      }
     </script>
 
     <script type="module">
diff --git a/packages/@ember/-internals/deprecations/index.ts b/packages/@ember/-internals/deprecations/index.ts
index 2e3ed564e3f..91a2f2510f4 100644
--- a/packages/@ember/-internals/deprecations/index.ts
+++ b/packages/@ember/-internals/deprecations/index.ts
@@ -129,6 +129,16 @@ export const DEPRECATIONS = {
       enabled: '5.10.0',
     },
   }),
+  DEPRECATE_ARRAY_PROTOTYPE_EXTENSIONS: deprecation({
+    id: 'deprecate-array-prototype-extensions',
+    url: 'https://deprecations.emberjs.com/id/deprecate-deprecate-array-prototype-extensions',
+    until: '6.0.0',
+    for: 'ember-source',
+    since: {
+      available: '5.10.0',
+      enabled: '5.10.0',
+    },
+  }),
 };
 
 export function deprecateUntil(message: string, deprecation: DeprecationObject) {
@@ -144,3 +154,14 @@ export function deprecateUntil(message: string, deprecation: DeprecationObject)
   }
   deprecate(message, deprecation.test, options);
 }
+
+const { EXTEND_PROTOTYPES } = ENV as {
+  EXTEND_PROTOTYPES: { Array?: boolean };
+};
+
+if (EXTEND_PROTOTYPES.Array !== false) {
+  deprecateUntil(
+    'Array prototype extensions are deprecated. Follow the deprecation guide for migration instructions, and set EmberENV.EXTEND_PROTOTYPES to false in your config/environment.js',
+    DEPRECATIONS.DEPRECATE_ARRAY_PROTOTYPE_EXTENSIONS
+  );
+}