Sprint has finally rolled out since yesterday the official Android 6.0 Marshmallow update over the air (OTA) to its HTC One M9 phones. The update will continue to be out until all of Sprint's One M9 units received it. Meanwhile, release for Verizon, AT&T, T-Mobile and US Cellular are poised coming this month as well.

HTC One M9 phones under Sprint have finally received the Android 6.0 Marshmallow update yesterday, a week later that what had been announced by the brand on Twitter last month. The update is expected to come in the next few days or weeks to One M9 units of other carriers in the United States like AT&T, Verizon, T-Mobile and US Cellular.

Canadian carriers first took the pilot release of Android 6.0 to One M9 units. As revealed by HTC's senior vice president for product management, Mo Versi, last week, Sasktel, Rogers, Wind and Videotron would first get the update.

Android 6.0 Marshmallow brings in two major improvements in Android Run Time (ART) and flex storage, among many other new features and improvements.

The Android Run Time gets prominent improvements since its debut in Android 4.4 KitKat, when it was still an optional feature. With Lollipop, the Android RT revolved with a Default setting instead of Dalvik cache to advance performance and help manage RAM usage. With Marshmallow, the feature will improve the performance of the device and also helps control battery consumption. In the first maintenance release of Marshmallow, the feature is expected to bring more improvements.

Flex storage is a combined storage feature for internal and external space, which makes it applicable only to devices with micro SD slot. With Marshmallow, it can format external memory card and pool to internal storage so that users can utilize to install apps and app data. However, slower memory card may trigger a low speed warning.