According to a post on WordPress.org, the WordPress 4.5 Beta is now available for testing.

WordPress 4.5 Beta 1

“WordPress 4.5 is slated for release on April 12, but to get there, we need your help testing what we have been working on, including:

  • Responsive Preview of your site in the Customizer (#31195) – See how your site looks in mobile, tablet, and desktop contexts before making changes to its appearance.
  • Theme Logo Support (#33755) – Native support for a theme logo within the Customizer.
  • Inline Link Editing (#33301) – Within the visual editor, edit links inline for a smoother workflow.
  • Additional Editor Shortcuts (#33300) – Includes a few new shortcuts, like `..` forcode and **..** for bold.
  • Comment Moderation Improvements (#34133) – An enhanced experience when moderating comments, including preview with rendered formatting.
  • Optimization of Image Generation (#33642) – Image sizes are generated more efficiently and remove unneeded meta, while still including color profiles in Imagick, for reduced sizes of up to 50% with near identical visual quality.”