[14] Instead of waiting over a year to add new features to Windows Phone 8, Microsoft opted to release three incremental updates to its existing mobile OS.

The updates included GDR2 (Lumia Amber), which introduced features such as "Data Sense",[15] and GDR3 (Lumia Black), which brought support for quad-core processors, 1080p high-definition screens of up to six inches, the addition of a "Driving Mode," and extra rows of live tiles for larger "phablet" devices.

The final shipping code was released to registered users of the "Preview for Developers" program on April 14, 2014,[5] and to the general public in subsequent months, the actual release date being determined by the devices' wireless carriers and accompanied with firmware updates, including Lumia Cyan.

[17] Users of the "Preview for Developers" program do not void their warranty in most cases and can install any future firmware that is included with their carrier's official rollout of Windows Phone 8.1.

Windows Phone 8.1 introduces a host of notable new features, most of which were unveiled in a preview released to developers on February 10, 2014.

[18] Cortana is a personal virtual assistant that was added in Windows Phone 8.1, and is similar to Google Now and Apple's Siri.

The Cortana name derives from the Halo video game series, which is a Microsoft franchise exclusive to Xbox and Windows.

Cortana's features include being able to set reminders, recognize natural voice without the user having to input a predefined series of commands and answer questions using information from Bing (like current weather and traffic conditions, sports scores, and biographies).

The updated browser also includes a new HTML video web player with support for inline playback and closed captions,[23] Windows 8-style website live tiles, and the ability to save passwords.

Applications built for WP8.1 can invoke semantic zoom, as well as access to single sign-on with a Microsoft account.

App collections, which were previously visible in a different page, are now fully featured on the front column of the Store.

[30] Storage Sense lets users move files and apps between their phone's hard drive and a microSD card, and incorporates features previously available in the "Settings" section that gave users the ability to delete temporary files to free up storage and uninstall applications.

Local Scout, which has been removed from Windows Phone 8.1 in the United States due to the implementation of Cortana, has been moved to Maps.

In addition to a large photo of the contact, text with the user's name and phone number now appear at the top of the screen instead of directly above the dialer.

[25] Additionally, users can now save high-resolution photos directly to OneDrive, instead of only having the option to upload the 5MP version of the image to the cloud.

The new notifications area's design allows the user to for example change wireless networks, turn Bluetooth and Airplane Mode on or off, and access "Driving Mode" from four customisable boxes at the top of the screen, while beneath these four horizontally placed boxes include recent text messages and social integration.

[35] The keyboard was touted for its speed and accuracy, and brought fame to Microsoft's research division when fifteen-year-old Lakeside School student Gaurav Sharma, using a Nokia Lumia 520 equipped with Windows Phone 8.1 and the "Word Flow" keyboard, broke the Guinness World Record for the world's fastest typing on a mobile phone, which was previously held by a Samsung Galaxy S4 user, by eight seconds.

As a result of this change, multiple file explorer apps have been released on the Windows Phone Store since the operating system's debut.

[47] In addition to these changes, SkyDrive has been completely rebranded to OneDrive across the operating system after Microsoft's settlement of a dispute over the "Sky" trademark with BSkyB.

Users are also presented with multiple options when a Windows Phone 8.1 device is connected to a computer via USB.

[18] Windows Phone 8.1 devices were manufactured by Microsoft Mobile (formerly Nokia) and its hardware partners, including HTC, Gionee, JSR, Karbonn, Micromax, Samsung, Alcatel,[48] Lava (under both the Lava and Xolo brands), Cherry Mobile, and Blu.

Sony (under the Xperia or Vaio brand) has also stated its intention to produce Windows Phone devices in the near future, but this has not materialized.

However, he commends Windows Phone for its ability to run smoothly across a wide variety of hardware and the thoughtful addition of features.