New Twiddle

components.test-component.js

import Component from '@ember/component';
import { or, readOnly } from '@ember/object/computed';
import { observer } from '@ember/object';

export default Component.extend({
  unwrappedApi: or('api.api', 'api'),

  foo: readOnly('unwrappedApi.foo'),
  bar: readOnly('foo.bar'),

  fooObserver: observer('bar', function() {
    console.log('bar changed');
  })
});

controllers.application.js

import Controller from '@ember/controller';
import { computed } from '@ember/object';

export default Controller.extend({
  api: computed(() => {
    return {
      api: {
        foo: {
          bar: 123,
        },
      },
    };
  }),

  actions: {
    updateApi() {
      this.set('api', {
        api: {
          foo: {
            bar: 456,
          },
        },
      });
    },
  },
});

templates.application.hbs

{{outlet}}

{{test-component api=api}}

<button {{action 'updateApi'}}>
  Update API
</button>

templates.components.test-component.hbs

{{bar}}

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "release",
    "ember-template-compiler": "release",
    "ember-testing": "release"
  }
}