This is the first public Windows 10 mobile pre-release build. It includes various changes from the operating system's predecessor, Windows Phone 8.1. The changes include an updated Start Screen where the wallpaper is displayed behind translucent tiles rather than within them and Live Tiles that can has a new tall size option for apps that support it. This feature would be removed in subsequent builds.^[4] Further changes to the Start screen includes app list redesigned with wallpaper as background, recent installed apps being shown at top, and the ability to search for apps though a prominent search box rather than a search button.^[5][6]

Other changes include changes to the general user experience, including the ability to expand notifications, actionable notifications,^[7] Action Center with additional settings toggles and same design across Windows 10 devices. The keyboard has been updated to contains virtual pointing stick for text selection and a voice input button.^[5] With this build, notifications can be synchronized between other Windows 10 devices. Furthermore, pressing and holding on any toggle in Action Center takes the user to respective settings of that option^[8] When shutting down the device the OS displays a reminder of coming calendar events on screen^[4][6][9]

Security features for this build include device encryption option.

New apps included in this build include a new file explorer app,^[10] an Alarms app, adding world clock, timer, and stopwatch modes,^[11] and a calculator app with a built in unit converter,^[12] The web browser rendering engine of Microsoft Edge is hosted in Internet Explorer, with the intention of Internet Explorer being replaced by Microsoft Edge in later builds.^[13] The system's default camera app is now an updated version of the Lumia Camera app. Other apps include the photos app with OneDrive synchronization, collections and automatic photo enhancements, and the universal Sound recording app. The operating system also introduces the universal Settings app ported from the PC version.^[4][6]

Microsoft introduces the Reachability feature for 5" devices and above, allowing users to press and hold the Windows button for entire screen to slide down fore easier reach topmost UI elements. Battery Saver now displays detailed information on an application's battery usage concerning lighting up the screen, running the processor or transferring data^[19]

The settings app offers Split-view when in landscape mode on higher-res displays, offering a UI almost identical to that on the PC^[20]

"Project Spartan" web browser adds the following features: InPrivate mode, secure sites – marked with a badge, full-screen videos, a "Save as" option for web images to convert files into .png or .jpg images ^[21] (in later betas, and released Windows 10, this app is branded as Microsoft Edge)

Other changes include 3G only setting for highest connection speed, more improvements to Cortana, the ability enable and disable OneDrive backups for individual applications, Digital video stabilization, and VPN Point to Point Tunnelling Protocol (PPTP) and Secure Socket Tunnelling Protocol (SSTP).

This build also has several minor UI changes, including the All Apps letter 'jump' buttons are ALL CAPS instead of lower case, search box replacing the search button at the top of the all apps list

Internet Explorer Mobile is removed from this build.

"Project Spartan" is now branded as Microsoft Edge. Microsoft Edge gained option to view a website as "desktop" or "mobile". The browser's address bar moved to bottom of the screen

This build brings updated icons and visuals (including visual controls). Flashlight toggle is added as a quick action in the Action Center.^[24] Quiet hours now has to be enabled from Cortana's notebook. Option for hiding notification panes on the lockscreen has been added. Finally, download limit on 3G networks removed.

The Photos app now shows albums (Camera roll, screenshots, saved photos);it also gained support for opening .gif files. Automatic camera roll back up is now enabled from the OneDrive application. The built-in camera application now supports Face detection^[25]

This build also adds support for HTTP Live Streaming.

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Slow ring:
July 22, 2015

This build finally removes the legacy Windows Phone 8.1 app store leaving only the Windows 10 version of the store app. Consequently, the Windows 10 store app loses the beta label.

Slow ring:
November 9, 2015

Public release:
November 12, 2015

This is the first Released to Manufacturing (RTM) build of Windows 10. It was released to device manufacturers to be preloaded on their devices.

In this build BitLocker adds support for XTS-AES encryption algorithm.^[31] Other security related features include Enhanced Credential Guard.^[32] In the Settings app, under Privacy, Call History and Email are now included.^[33] Starting with this build, Windows Spotlight is available on the Windows 10 Pro edition.

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This cumulative update brings improved UI for tracking data under Networking and Wireless > Data Usage in the Settings app.

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This update enables UWP games and apps to unlock framerate. This will allow UWP games to disable V-Sync and enable the use of third party features such as G-Sync and Freesync.^[62][63]

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• New music search icon in Cortana
• Improvements to Microsoft Edge and Messaging + Skype
• Reliability improvements for keyboards with large dictionaries

• New Visual Voicemail feature for dual-SIM devices
• Re-enabled history feature in People app

• Improvements to the Phone, Outlook Mail and Calendar apps

• Improvements to Microsoft Edge
• New Japanese one-handed kana touch keyboard
• New Feedback Hub app
• Improvements to Word Flow recognition of longer words

Slow ring:
March 30, 2016

• Improvements to the Action Center, Notifications, Cortana, Microsoft Edge and Lock screen experience
• Updated the Settings app
  • New icons for individual settings pages
  • New Navigation bar settings page and vibration setting
  • Updated Battery Settings and Battery Saving Experience
  • Glance screen settings have moved
  • Updated Windows Update Settings
• New emoji
• Added USB Ethernet Support with Continuum
• New comment feature in the Feedback Hub

• New Messaging Everywhere feature
• Enabled Cortana for more languages

• Improvements to Start experience

• Improvements to the share UI for Cortana Reminders
• Reliability improvements to the Chinese IME

Slow ring:
May 31, 2016

• New swipe navigation feature in Microsoft Edge
• New Apps for websites feature
• Improvements to Feedback Hub
• Increased font size and improved spacing of the data migration page
• Polished media controls interface on the Lock screen
• Improved performance when retrieving updated GPS coordinates while driving

• Improvements to Cortana and Glance screen
• Updated the UI for rearranging Quick Actions in the Settings app
• Updated thumbnail generation logic
• Updated the Mobile Hotspot settings page
• Reliability improvement to Cortana

• Improvements to Settings
• Polished the notification dismissal model
• Reliability improvement to Cortana
• Introduced one-handed keyboard for 5-inch devices

• Minor visual enhancements to the Settings app

Slow ring:
June 21, 2016

• New Microsoft Wallet app

Slow ring:
June 28, 2016

• Updated the Gadgets app
• Messaging Everywhere has been removed from the Messaging app

• Improved battery performance for turning the screen on and off to look at the lock screen

• Improved battery performance on older devices

Slow ring:
July 15, 2016

Slow ring:
July 20, 2016 Release preview:
July 28, 2016

Slow ring and release preview:
July 28, 2016

Public release:
August 16, 2016