diff --git a/packages/@ember/-internals/metal/index.ts b/packages/@ember/-internals/metal/index.ts
index 4b838b51aad..8e4d54a3dbf 100644
--- a/packages/@ember/-internals/metal/index.ts
+++ b/packages/@ember/-internals/metal/index.ts
@@ -38,6 +38,7 @@ export {
 } from './lib/descriptor_map';
 export { watchKey, unwatchKey } from './lib/watch_key';
 export { ChainNode, finishChains, removeChainWatcher } from './lib/chains';
+export { getChainTagsForKey } from './lib/chain-tags';
 export { watchPath, unwatchPath } from './lib/watch_path';
 export { isWatching, unwatch, watch, watcherCount } from './lib/watching';
 export { default as libraries, Libraries } from './lib/libraries';
@@ -53,7 +54,7 @@ export {
 } from './lib/observer';
 export { Mixin, aliasMethod, mixin, observer, applyMixin } from './lib/mixin';
 export { default as inject, DEBUG_INJECTION_FUNCTIONS } from './lib/injected_property';
-export { tagForProperty, tagFor, markObjectAsDirty } from './lib/tags';
+export { tagForProperty, tagFor, markObjectAsDirty, UNKNOWN_PROPERTY_TAG } from './lib/tags';
 export { default as runInTransaction, didRender, assertNotRendered } from './lib/transaction';
 export { Tracker, tracked, getCurrentTracker, setCurrentTracker } from './lib/tracked';
 
diff --git a/packages/@ember/-internals/metal/lib/tags.ts b/packages/@ember/-internals/metal/lib/tags.ts
index 56b412790f4..57b08f612ed 100644
--- a/packages/@ember/-internals/metal/lib/tags.ts
+++ b/packages/@ember/-internals/metal/lib/tags.ts
@@ -1,5 +1,5 @@
 import { Meta, meta as metaFor } from '@ember/-internals/meta';
-import { isProxy } from '@ember/-internals/utils';
+import { isProxy, symbol } from '@ember/-internals/utils';
 import { EMBER_METAL_TRACKED_PROPERTIES } from '@ember/canary-features';
 import { backburner } from '@ember/runloop';
 import { DEBUG } from '@glimmer/env';
@@ -12,6 +12,8 @@ import {
   UpdatableTag,
 } from '@glimmer/reference';
 
+export const UNKNOWN_PROPERTY_TAG = symbol('UNKNOWN_PROPERTY_TAG');
+
 function makeTag(): TagWrapper<DirtyableTag> {
   return DirtyableTag.create();
 }
@@ -23,7 +25,11 @@ export function tagForProperty(object: any, propertyKey: string | symbol, _meta?
   }
   let meta = _meta === undefined ? metaFor(object) : _meta;
 
-  if (isProxy(object)) {
+  if (EMBER_METAL_TRACKED_PROPERTIES) {
+    if (!(propertyKey in object) && typeof object[UNKNOWN_PROPERTY_TAG] === 'function') {
+      return object[UNKNOWN_PROPERTY_TAG](propertyKey);
+    }
+  } else if (isProxy(object)) {
     return tagFor(object, meta);
   }
 
diff --git a/packages/@ember/-internals/runtime/lib/mixins/-proxy.js b/packages/@ember/-internals/runtime/lib/mixins/-proxy.js
index f895fa4d95e..3e5ed0d5316 100644
--- a/packages/@ember/-internals/runtime/lib/mixins/-proxy.js
+++ b/packages/@ember/-internals/runtime/lib/mixins/-proxy.js
@@ -14,6 +14,8 @@ import {
   Mixin,
   tagFor,
   computed,
+  UNKNOWN_PROPERTY_TAG,
+  getChainTagsForKey,
 } from '@ember/-internals/metal';
 import { setProxy } from '@ember/-internals/utils';
 import { EMBER_METAL_TRACKED_PROPERTIES } from '@ember/canary-features';
@@ -85,6 +87,10 @@ export default Mixin.create({
     }
   },
 
+  [UNKNOWN_PROPERTY_TAG](key) {
+    return getChainTagsForKey(this, `content.${key}`);
+  },
+
   unknownProperty(key) {
     let content = contentFor(this);
     if (content) {