Disable all new keywords behind a feature flag

Author: NullVoxPopuli

packages/@ember/canary-features/index.ts

@@ -13,6 +13,7 @@ import { ENV } from '@ember/-internals/environment';
 
 export const DEFAULT_FEATURES = {
   // FLAG_NAME: true/false
+  NEW_KEYWORDS_2026_05: true,
 };
 
 /**
@@ -55,12 +56,14 @@ export function isEnabled(feature: string): boolean {
 
 // Uncomment the below when features are present:
 
-// function featureValue(value: null | boolean) {
-//   if (ENV.ENABLE_OPTIONAL_FEATURES && value === null) {
-//     return true;
-//   }
+function featureValue(value: null | boolean) {
+  if (ENV.ENABLE_OPTIONAL_FEATURES && value === null) {
+    return true;
+  }
 
-//   return value;
-// }
+  return value;
+}
 //
 // export const FLAG_NAME = featureValue(FEATURES.FLAG_NAME);
+
+export const NEW_KEYWORDS_2026_05 = featureValue(FEATURES.NEW_KEYWORDS_2026_05);

packages/@ember/template-compiler/lib/plugins/auto-import-builtins.ts

@@ -1,6 +1,7 @@
 import type { AST, ASTPlugin } from '@glimmer/syntax';
 import type { EmberASTPluginEnvironment } from '../types';
 import { isPath, trackLocals } from './utils';
+import { NEW_KEYWORDS_2026_05 } from '@ember/canary-features';
 
 /**
  @module ember
@@ -14,6 +15,13 @@ import { isPath, trackLocals } from './utils';
 */
 
 export default function autoImportBuiltins(env: EmberASTPluginEnvironment): ASTPlugin {
+  if (!NEW_KEYWORDS_2026_05) {
+    return {
+      name: 'auto-import-built-ins-disabled',
+      visitor: {},
+    };
+  }
+
   let { hasLocal, visitor } = trackLocals(env);
 
   return {