After 3.5 years and 28 minor releases, Ember 3.28 marks the end of the project's 3.x series.
To ensure a smooth upgrade path going into the 4.x series, 3.28 has been declared an LTS (Long Term Support) candidate. In six weeks,
the latest patch version of 3.28 will be promoted to be the latest LTS release
and replace 3.24-LTS.
We're also announcing the start of the Ember 4.0 beta cycle for all sub-projects. Following the process set in previous major versions, Ember 4.0's beta introduces no new features. Instead, it removes support for deprecated public APIs. We encourage our community (especially addon authors) to help test beta builds and report any bugs before they are published as a stable release in six weeks' time. We also encourage everyone to help maintainers resolve deprecations in their favorite addons. The ember-try addon is a great way to continuously test your projects against the latest Ember releases.
Developers who want to prepare for the upcoming 4.0 version of Ember should work to resolve all deprecation warnings in their apps and addons while using Ember 3.28.
An app or addon with no deprecation warnings on Ember 3.28 should be able to upgrade from Ember 4.0 without making significant changes outside of the
dependency versions.
You can read more about Ember's plans for 4.0 in The Road to Ember 4.0.

Ember.js
Ember.js is the core framework for building ambitious web applications.
Changes in Ember.js 3.28
Ember.js 3.28 is an incremental, backwards compatible release of Ember with bug fixes, performance improvements, and a minor deprecation fix. 3.28 introduces no new features, helping to ensure the final release of the 3.x cycle is stable and battle-tested.
For the full set of changes (including 7 bug fixes), see the Ember.js 3.28.0 release page on GitHub.
In Ember 3.24, various string methods added to the String.prototype were deprecated for removal in Ember 4.0. htmlSafe (the version available via string prototype) was supposed to be included in those deprecations, however it was overlooked. This omission is corrected in 3.28.

Ember Data
Ember Data is the official data persistence library for Ember.js applications. The changes introduced in Ember Data 3.28 focus on bug fixes and refactors in preparation for 4.0.
Changes in Ember Data 3.28
Improvements to relationship materialization & unloading performance
A number of performance improvements were shipped in Ember Data 3.28, including
significant improvements to relationship materialization and unloading performance
via emberjs/data#7491 and
emberjs/data#7493. In particular,
the performance improvements should be notable when loading large sets of data.
See the PRs linked above and changelog for further notes on performance improvements.
Unload records from the store when calling destroyRecord
destroyRecord would previously leave the deleted record in the store. This
could cause issues if IDs were re-used, or could require extra filtering to
confirm that destroyed content was not in an array of models.
3.28 will unload records from the store when destroyRecord is called. For more
details, see emberjs/data#7258 and
the GitHub issues mentioned in the PR.
Custom Model Classes
Used conventionally, Ember Data blends the definition of a model's schema and
record API into a single JavaScript class. For example:
import Model from '@ember-data/model';

export default class PersonModel extends Model {
/*
* Define a schema
*/
@attr('string') firstName;
@attr('string') lastName;

/*
* Define an API on the record instance
*/
get fullName() {
return `${this.firstName} ${this.lastName}`;
}
}

Ember Data 3.28 introduces the ability to separate model schema and record instance
class definitions. This is a low-level capability that we expect addon authors
to use when they experiment in these areas (possibly others):
First, forcing the definition (statically or at runtime) of a distinct class for
every model can cause performance issues. Large applications may have hundreds
of models. If most or all of these models do not require unique classes, we're
generating more memory load and asking more of the JIT's type system than
they may be necessary. In the extreme case, it may be possible for all record
instances in an application to share a single root class.
Second, the current Ember Data schema definition API forces definitions to be authored in
JavaScript. Removing that limitation allows us to experiment with more optimal
or powerful ways to encode schema (such as JSON). These alternatives may perform
better (in payload size, or in parse/eval), may better support generation and
synchronization with API typing systems, and better support static analysis
(for example, with TypeScript).
For further details on these new capabilities, refer to:

• RFC #487: Custom Model Class
• RFC #466: Request State Service
• RFC #463: Record State on RecordData
• RFC #463: RecordData Errors

Much of this API surface is already used by the
ember-m3 project, which provides an
alternative model class for Ember Data.
Bug Fixes
Ember Data 3.28 introduced 12 bug fixes and some internal refactors. For the full set of changes, see the CHANGELOG.md.

Ember CLI
Ember CLI is the command line interface for managing and packaging Ember.js applications.
Changes in Ember CLI 3.28
Drop Node 10 support
Ember CLI 3.28 drops support for Node 10. Node 10 became end of life (it no longer receives security updates) in April 2021.
Introducing ember-addon.projectRoot
This new configuration option allows you to run ember serve from outside of a project's root directory. For example, if you're using yarn workspace or a monorepo and want to support running ember serve from the root of the repo, update the top-level package.json to include the following config:
{
"ember-addon": {
"projectRoot": "./packages/path-to-ember-project"
}
}

For more details on the changes in Ember CLI 3.28 and detailed upgrade
instructions, please review the Ember CLI 3.28.0 release page.
Upgrading Ember CLI
You may upgrade Ember CLI using the ember-cli-update project:
npx ember-cli-update

This utility will help you to update your app or addon to the latest Ember CLI version. You will probably encounter merge conflicts, in which the default behavior is to let you resolve conflicts on your own. For more information on the ember-cli-update project, see the GitHub README.
While it is recommended to keep Ember CLI versions in sync with Ember and Ember Data, this is not required. After updating ember-cli, you can keep your current version(s) of Ember or Ember Data by editing package.json to revert the changes to the lines containing ember-source and ember-data.
Thank You!
As a community-driven open-source project with an ambitious scope, each of these releases serves as a reminder that the Ember project would not have been possible without your continued support. We are extremely grateful to our contributors for their efforts.