It’s a whole new world.
Powered by Yii 2
Yii 2 has been completely rewritten to utilize new PHP features like traits, namespaces, and late static bindings, and it adds some great new features of its own including PSR-4-compliant autoloading support, dependency injection, better error handling, and improved performance and security.
Craft 3 makes it possible to manage multiple sites under the same Craft installation. Each site gets its own base URL and language, and your content can be targeted and translated on a per-site basis. Best of all, multi-site management is available to all Craft editions (even Personal), and sites don’t come with an added cost.
Inspired by Yii 2, we’ve refactored Craft’s entire codebase to more closely follow Yii’s conventions and take advantage of more of Yii’s built-in functionality. As a result Craft is now significantly faster, leaner, and simpler.
TTFB (time-to-first-byte) is generally about twice as fast as Craft 2.
75% Less Memory
Typical requests consume about 75% less memory than Craft 2.
Plugins have always shared a likeness with Craft, but the similarities have been mostly superficial. That changes in Craft 3 though. Now plugins are implemented as modules, so they can have their own controllers, views, sub-modules, and service components, all powered by the same code that gives Craft itself those features.
Asset Sources have been renamed to “Volumes” in Craft 3, and their API has been dramatically simplified. In addition to Craft’s built-in Local, S3, Google, and Rackspace Volume types, plugins are now able to supply their own. There’s even a base Volume class that makes it really easy to implement Flysystem-based Volume types.
Powerful Content Querying
ElementCriteriaModel is dead! In its place: ElementQuery. With ElementQuery you can still query for elements in the same way you did in Craft 2, but with some great new features. It's now possible to make changes to the actual SQL query that will get executed, and you have more choices on how the data should be returned.
We’ve included the Yii 2 Debug Extension, giving Admins a clear picture of what’s going on behind the scenes. You can see details about your server environment and incoming HTTP requests, view logs, deprecation errors, profiling reports, database queries, and more. Just enable the Debug Toolbar from your user account’s settings.
The Future of Plugin Dev
Brandon Kelly explains the development changes coming to Craft 3 in this 80-minute workshop recorded at Peers 2015.