WordPress 5 was released on December 6, 2018. This major release includes the new block editor, aka Gutenberg, the most significant change to the WordPress editing experience since WYSIWYG was added.
On Thursday, December 20, we deployed WordPress 5.0 to our multisite network. However, we network activated the Classic Editor plugin. With this plugin active, the editing experience is unchanged from previous versions of WordPress. Site admins have the ability to override this plugin on an individual site under the Writing settings in the WordPress dashboard.
If the new block editor is enabled, the content on existing posts and pages is placed into a "Classic Block." A classic block can be left as-is, or it can easily be converted to the new Gutenberg blocks, where each paragraph, image, embed, etc. is a separate block.
We highly recommend watching the "WordPress 5 Essential Training" video course at Lynda.com before enabling the new block editor.
Also, be aware that the accessibility level of the new editor is currently unclear, and those who rely on keyboard navigation, rather than touch or a mouse, could experience difficulty trying to create content.
WordPress 5.0 comes with the new Gutenberg-optimized Twenty Nineteen theme. The new block editor should work with most existing themes, but some content, such as full-width images, might be constrained by the limitations of that theme. We will be adding more Gutenberg-ready themes in the coming months.