After a series of Lollipop updates for its more recent Xperia devices, Sony has finally rolled out its Android 5.1.1 firmware upgrade for its two-year old flagship lineup, Xperia Z1, Z1 Compact and Z Ultra smartphones.

According to XperiaBlog.net, a Sony-focused tech site, Android 5.1.1 Lollipop with build number 14.6.A.0.368 is now distributed over-the-air (OTA) to all three Xperia models. The report cited sources who claims that the update is only available on select regions at the moment.

It is also worth adding that the new software update will mainly bring in bug fixes so users should not expect a lot of new features included. However, if this is similar or part of the previous Android 5.1 Lollipop updates that the Japan-based manufacturer release for the wider Xperia Z range, then the patch will also be comprised of some new customization options like camera improvements, enhanced enterprise support, and SmartWear integration.

As mentioned, the upgrade is live in a handful of countries but it is expected to roll out all over the world in due time. It is understandable given that the firmware is being sent in stages. It means that it may take a few weeks until all users will get the update. They can also expect this software to address the much hyped Stagefright vulnerability.

Owners of the abovementioned Sony handsets can also keep an eye out for the OTA update notification or alert on their smartphones. Alternatively, they may also check out the company's PC Companion software to see if a manual download is already available.

Here is the full Android 5.1.1 Lollipop changelog for the Sony Xperia Z1, Z Ultra, and Z1 Compact.

• Improvements to volume and silent mode control, more control of alerts; simplified and enhanced design
• Integration of LinkedIn with Calendar and Contacts
• Camera focus, speed and accuracy improvements in Superior Auto mode
• Many new features for Xperia in Business, enhancing enterprise support for Xperia
• Updated camera features using Sony SmartWatch 3; the SW3 can now be used as a remote shutter button
• Instant calendar events - create & share smart events directly from any email
• Calendar agenda in Email - no need to switch apps to check upcoming events
• Richer Xperia themes
• New Settings menu icons
• Additional options for Wi-Fi and Bluetooth in notification menu

Apart from these Android 5.1.1 updates, Sony is also predicted to release the upcoming Android 6.0 Marshmallow OS to its Xperia range. But it is only expected to be for the most recent Xperia Z3+ and Z3 line, it remains to be seen whether the device maker will update the Xperia Z1 and its sibling models, which had been released back in 2013.