Beyond the sweet addi­tion pic­tured above, this is the biggest update since 3.x:

• Improves per­for­mance when open­ing large libraries.
• Addresses per­for­mance issues when export­ing heavily-adjusted images, par­tic­u­larly those with Highlights & Shadows, Definition, Noise Reduction, Edge Sharpen, Sharpen, Skin Smoothing, or Blur.
• Addresses per­for­mance when using Core Image fil­ters such as Curves, Levels, and Highlights & Shadows.
• The appli­ca­tion now dis­plays a progress dia­log when open­ing or switch­ing between libraries.
• Addresses qual­ity issues in con­nec­tion with ren­der­ing of images scaled to below 100% in the Viewer.
• Fixes an issue that could cause images exported as TIFFs to have an incor­rect dpi setting.

Download from soft­ware update, or man­u­ally here