Windows 10 build 10074 released to Fast and Slow Ring Insiders

General UI improvements throughout including a new Live Tile animation on the Start Menu.

Improved high DPI display support.

An A/B test is in place for the return of Aero Glass and if it is widely accepted it could return in other areas of the OS and not just in the Start Screen/Menu transparency.

Continuum gets the simplified taskbar we saw in today's keynote demo and closing an app returns to the Start Screen in Tablet Mode.

Improvements with multi-tasking with  Alt-Tab, Task-View, and Snap Assist.

Updated default Windows sounds.

Cortana visual changes as shown during the Day 1 keynote. She also gets some Bing Instant Answers integration and several new questions she can answer.

Updates to Music, Video and Xbox Apps

Windows Store Beta, now with the Blue tile, has been expanded to 41 markets and Xbox Live games and in app purchases should be working.

You can now launch Win32 (desktop) apps from the Start menu again. 

You should be able to download music in the Xbox Music and Music Preview apps.

When you minimize an app playing audio, it should continue playing in the background.

Developers cannot enable Developer Mode in the Settings app for installing and testing apps on this build. We’ll enable this in an upcoming build. In the meantime, you will need enable your device for development using the Group Policy Editor.

There is an issue in this build preventing some games from playing in full screen mode. We’re working to get a fix out via WU as soon as possible.

The People app continues to crash. We’re planning to release an update for the People app through the Store Beta that fixes this.