Microsoft has released a new build of Windows 10 to Windows Insiders who set their preview builds update preference to be on the fast track. Windows Insiders who are on the fast ring receives newer public builds of Windows 10 faster than those on the slow ring, at the expense of more bugs and instability.

The new April 2015 build of Windows 10 released in build 10061, fulfilling the promise of faster new builds release. Windows 10 Build 10061 was preceding by Windows 10 Build 10049, which revealed Project Spartan new web browser. Main highlights of Windows 10 Build 10061 are new black system theme across the Start menu, Taskbar, and Action Center, and the new updated universal Mail and Calendar apps, though it’s known that the version of the Mail and Calendar apps included in this build (17.4008.42281.0) have a known issue that causes every typed letter to appear twice, and should be (and will be) updated to version 17.4016.42291.0 through Windows Store Beta.

Gabe Aul detailed the changes in Windows 10 Build 10061:

  • New Mail and Calendar apps: These new apps bring improved performance and a familiar three-pane email UI, with a toggle to quickly move between your email and calendar. Mail includes customizable Swipe Gestures, letting you swipe right or left to take actions like delete, flag, move or mark as read/unread. Also check out the new email authoring experience. Mail leverages the familiar and rich capability of Word to that allows you to easily insert tables, add pictures and use bullets and color to your text. Both the new Mail and Calendar apps support Office 365, Exchange,, Gmail, IMAP, POP and other popular accounts.
  • Start, Taskbar, and Action Center improvements: This build introduces the new black system theme across the Start menu, Taskbar, and Action Center. The Start menu and Taskbar now have transparency and you can also resize the Start menu. We’ve also enabled support for AutoColor which pulls the primary color from your desktop background. In the Settings app under Personalization, you can adjust the color of Start, Taskbar, and Action Center as well as transparency. Check these settings out and let us know what you think. And based on your feedback, we have moved the power button to the bottom left from the top right of the Start menu to make it more accessible.
  • Continuum improvements: The Taskbar is now more optimized for tablets. Entering Tablet Mode causes the Start button, Cortana, and the Task View buttons to all grow in size and space out to be more touchable. Items in the Notification area also widen to improve touchability. Also, pinned and running apps are removed by default to reduce clutter and simplify the experience. Start and Task View remain available for launching and switching. If you still prefer to see apps on your taskbar, there is an option under Tablet Mode in Settings to turn them back on. We also now offer a setting to boot directly into Tablet Mode. For tablets under 10 inches, this is the default behavior.
  • Task View improvements: We’ve made several visual updates to Task View. We’ve refined the window icons, the close buttons, and the thumbnails. These improvements also apply to Alt+Tab and Snap Assist. Task View gets a new icon on the Taskbar too.
  • Virtual Desktop improvements: You can create as many Virtual Desktops as you’d like! When you hit the limit of your display, a new overflow experience now lets you access any one of your desktops. Also, don’t forget that we are still eager to hear your feedback to determine the default behavior of the Taskbar across desktops.

Unfortunately, Microsoft won’t be officially releasing a new Windows 10 Technical Preview ISO images for builds on the fast ring. But you can create your own ISO image using the build 10061 ESD file downloaded from Windows Update. And there are plenty of Windows 10 Build 10061 ISO images now floating on the web.

Update: Windows 10 Insider Preview Build 10074