WordPress 4.2 includes both new and improved features. It also includes changes under the hood.  While I’m sure you’ve been testing your themes, plugins, and sites in preparation for the release, you may have missed the announcements of all the changes. Here is a quick rundown of developer related things you should know:

Source: WordPress › WordPress 4.2 Field Notes « Make WordPress Core

For the second release in a row, I put together some Field Notes to help developers for the Make WordPress Core blog.  The most fun thing I found is that in 4.2 231 bugs reported vs previous versions of WordPress were fixed. This is up from 174 in 4.1.  Every release WordPress improves.