Today, the Ember project is releasing version 3.13 of Ember.js, Ember Data, and Ember CLI.
Ember 3.13 is the final release of Ember before Octane. Ember 3.13 is also the Octane preview. The preview allows adventurous community members to start using its stable features and help put the final round of polish on supporting tools and documentation before Octane becomes official in 3.14. You can learn more about what to expect from Octane and how to prepare your apps in a previous blog post.
Additionally, version 3.12 of Ember is now promoted to LTS (Long Term Support). An LTS version of Ember continues to receive security updates for 9 release cycles (54 weeks) and bugfixes for 6 cycles (36 weeks). LTS releases typically occur every four minor versions. The previous LTS version of Ember was 3.8.
The Octane Preview
The Octane features in 3.13 are stable public APIs with our normal SemVer guarantees. If you build an app using APIs in the Octane preview, it will continue to work in future versions.
So why is this a preview and not the final Octane release?
A big part of Octane is about delivering an excellent developer experience, whether you are a beginner or a power user. While these APIs are stable, not all Octane features are compatible with popular addons yet. We are also still updating documentation, and important tools like the Ember Inspector do not yet work with some Octane features. Octane is not complete until these supporting pieces are in place.
Then, when Ember 3.14 arrives, Octane will be the recommended way to use Ember and new apps will have Octane's optional features enabled by default. The guides and tutorials will show Octane examples, and codemods will be available to help users migrate to Octane. Visit the Octane landing page for links to the learning resources, which are deployed to a temporary URL.
The Ember tutorial has already been completely rewritten for Octane, and the easiest way to understand the big picture of Octane, especially if you're already an experienced Ember developer, is to work through the new tutorial, which you can find through the Octane landing page.

You can try out the Octane preview by performing a few steps:
Add the following packages if they aren't already present at this version:
npm install --save-dev @ember/edition-utils@^1.1.1
npm install --save-dev @glimmer/component@^0.14.0-alpha.13

Disable legacy behavior by setting the following feature flags:
ember feature:disable jquery-integration
ember feature:enable template-only-glimmer-components
ember feature:disable application-template-wrapper

Specify the Octane edition in .ember-cli.js by adding the following lines to the beginning of the file:
// .ember-cli.js
const { setEdition } = require('@ember/edition-utils');

setEdition('octane');

If you have an .ember-cli file instead of an .ember-cli.js file, you can convert it by renaming it to .ember-cli.js, then taking the existing JSON object and assigning it to module.exports. For example, if you have an .ember-cli file with:
// .ember-cli
{
"disableAnalytics": false
}

The equivalent .ember-cli.js file would be:
// .ember-cli.js
module.exports = {
"disableAnalytics": false
}

If you need more information on how to migrate away from these legacy features, check out the Octane release plan blog post.

Ember.js
Ember.js is the core framework for building ambitious web applications.
Changes in Ember.js 3.13
Ember.js 3.13 is an incremental, backwards compatible release of Ember with bugfixes, performance improvements, and minor deprecations. There are five (5) new features, one (1) deprecation, and several bugfixes in this version.
New Features (5)
Tracked Properties and Tracked Property Updates (1 of 5)
Tracked properties introduce a simpler and more ergonomic system for tracking state change in Ember applications. Tracked properties allow Ember to reduce its API surface area while producing code that is both more intuitive and less error-prone.
Have a look at the [guides] to learn more about tracked properties. For design details, check out RFC 410 and RFC 478.
Component Templates Co-location: Part One (2 of 5)
Component co-location is available in Ember 3.13. This feature allows you to group a component's template and JavaScript files together in the file system. For example, a component named user-profile would be made up of the following files:
app
└── components
├── user-profile.hbs
└── user-profile.js

Note: Previously, in 3.13, this feature was not available unless you enabled the Octane preview. That changed once a performance issue was addressed.
The RFC contains a detailed explanation of the design of this feature.
component-class generator (3 of 5)
With the Octane preview enabled, a component generated using ember generate component will no longer include a component class by default.
In cases where you need a component class file, you can either pass the --with-component-class flag to the component generator, or add one after the fact with the new ember generate component-class generator.
Detect the edition that is in use (4 of 5)
For addon authors, it is now possible to detect which edition is in use at build-time with @ember/edition-utils.
import { has } from '@ember/edition-utils';

let isOctane = has('octane');

Add updateHook component-manager capability (5 of 5)
There is a new capability for component managers which allows you to opt-in or opt-out of whether to have an updateComponent hook on your component manager.
If you're not an addon author or maintain a component manager, then you are unlikely to need use this new feature.
Deprecations (1)
Deprecations are added to Ember.js when an API will be removed at a later date. Each deprecation has an entry in the deprecation guide describing the migration path to a more stable API. Deprecated public APIs are not removed until a major release of the framework.
Consider using the ember-cli-deprecation-workflow addon if you would like to upgrade your application without immediately addressing deprecations.
For more details on changes in Ember.js 3.13, please review the Ember.js 3.13.0 release page.
Deprecate support for mouseEnter/Leave/Move Ember events (1 of 1)
Ember.js 3.13 deprecates support for mouseEnter, mouseLeave and mouseMove Ember events. The deprecation guide contains guidance on how to migrate away from these events.

Ember Data
Ember Data is the official data persistence library for Ember.js applications.
Changes in Ember Data 3.13
New Features (0)
No new features introduced in Ember Data 3.13.
Deprecations (0)
No new deprecations introduced in Ember Data 3.13.
For more details on changes in Ember Data 3.13, please review the
Ember Data 3.13.0 release page.

Ember CLI
Ember CLI is the command line interface for managing and packaging Ember.js applications.
Upgrading Ember CLI

You may upgrade Ember CLI easily using the ember-cli-update project:
npm install -g ember-cli-update
ember-cli-update

This utility will help you to update your app or add-on 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.
Changes in Ember CLI 3.13
No new features in Ember CLI 3.13.

For more details on the changes in Ember CLI 3.13 and detailed upgrade
instructions, please review the Ember CLI 3.13.0 release page.
Ember 3.12 is an LTS Release
If you are upgrading from the previous LTS version (3.8) to 3.12 then you are getting access to these features:

• router service
• Support for native classes
• The array helper
• Element Modifier Manager (and modifiers in general)
• Nested angle bracket component invocation
• Angle bracket invocation for built-in components
• Support for native decorators
• The {{fn}} and {{on}} modifiers

3.14 Beta
This release kicks off the 3.14 beta cycle for all sub-projects. We encourage our community (especially addon authors) to help test these beta builds and report any bugs before they are published as a final release in six weeks' time. The ember-try addon is a great way to continuously test your projects against the latest Ember releases.
Among other things, the @model named argument will be available to route templates. While not officially an "Octane feature", this feature will available for the first time in the 3.14 release, which coincides with the Octane release. Since the Octane guides and documentation are targeting the same version, you will see them using this feature, but please note that the feature is not available in the 3.13 Octane preview.
This beta release also included a new debug render tree API, which will be integrated into the Ember Inspector sometime during the beta cycle to give it full Octane support.
You can read more about our general release process here:

• Release Dashboard
• The Ember Release Cycle
• The Ember Project
• Ember LTS Releases

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 the continued efforts of everyone in the community. We are extremely grateful to our contributors for their efforts.