According to WordPressThere is change in old theme called Twenty Fifteen.
Our beautiful new default theme, Twenty Fifteen. It’s a clean, mobile-first, blog-focused theme designed through simplicity.
In WordPress 4.1 a new distraction-free writing mode for the editor. Presently it is available for the beta version of the WordPress 4.1 This will help you to focus on writing. You will notice that the meta boxes and WordPress administrator bar will slide out of view and will remain hidden as long as you are writing. As soon as you move the cursor away from it, the administrator bar and meta boxes will slide back.
- The ability to automatically install new language packs right from the General Settings screen (available as long as your site’s filesystem is writable).
- A new inline formatting toolbar for images embedded into posts.