WordPress 3.8.3 was released on April 14, and WordPress sites with Auto Updates enabled should have been silently updated. In some cases, the 3.8.3 update may not have had time to auto-update before WordPress became available yesterday.

WordPress 3.8.3 fixes a minor bug that was introduced in the previous release, 3.8.2.

WordPress 3.9 makes several significant changes to the handling of media files, and makes it a bit easier for developers to experiment with widgets.

Neither release apparently includes any security fixes.