Over half of HTC One M9 units in the United States have finally been updated to Android 6.0 Marshmallow. However, units under AT&T and US Cellular remain stuck under the radar of Lollipop.

HTC One M9 units under AT&T and US Cellular are slated to receive the official Android 6.0 Marshmallow after a relatively long gap from Verizon, Sprint and T-Mobile's releases. HTC first released Marshmallow on its phones since the beginning of this year in Canada, UK, US and even to other countries.

There are no exact details as to when these mobile carriers will receive the Android 6.0 Marshmallow update on its HTC One M9 units. However, previous reports already stated that this will come in the first quarter of the year. If HTC will live up to its promise, One M9 shall receive the update this week. Meanwhile, both AT&T and US Cellular were not vocal about their plans for the device until now, but the update must come with a surprise.

In another news, amid this overdue update hullaballoo, HTC is said to be "working on catching up" as updates continued to roll out in China and some European countries. The latest HTC device to get Marshmallow is the Desire EYE in United Arab Emirates.

HTC's Marshmallow comes with the Sense 7.0 user interface (UI). Sense 7.0 UI brings a few enhancements to user customization, a wide variety of themes to choose from, flatter and simpler look and notification-based card. Also, the performance has one of the biggest changes brought by Sense 7.0 to the phone's chipset.

Marshmallow also comes with several bug fixes and a new and updated set of emojis. The Marshmallow launcher will come in with a whole lot of improvements in apps and software configurations, plus new and fresh features straight from Google dev. These include the battery saver named 'Doze', smarter Google Now with more accurate suggestions and recommendations, apps permissions, direct share, additional mobile payment systems like Google Pay, Visa, Discovery and MasterCard, and supports for Android Pay and fingerprint scanner, among many others.