The last time that the Padfone 2 got a major version update was way back in December 2012, for Jelly Bean 4.1. Yeah, you read that right. Today ASUS is updating its second phone-tablet-combo-thingy all the way to KitKat, a move that will surely please at least some of the users who haven't upgraded to one of the newer models. Are you ready for some sketchy ASUS English translations? Of course you are.
Screenshots via Rob Mey on Google+.
The 4.4 builds for Padfone 2 models sold in Japan, Russia, Taiwan, China, Singapore (StarHub), and the worldwide edition have all been released - you can download them at the source hub. ASUS recommends backing up your data "Due to this Android 4.4 upgrade would reset your device," and this upgrade guide (PDF link) confirms that the flash process WILL erase your personal data. The ASUS PC Tool (included on the download page) can be used to back it up to your PC, which is handy, since the update apparently isn't going out over-the-air.
PadFone2 Firmware: V22.214.171.124 Only for JP SKU (Android 4.4)
Steps of Update:
1. Check SW version of your PadFone2*
2. Download PadFone Firmware: V126.96.36.199 Only for JP SKU and Update version of SOP (From “Manual” Item)
※Firmware update cannot do *SKU conversion* and downgrade version.
Wrong SKU may cause update failure, You can only update your SW version on the Same SKU
*How to check SW version of your PadFone2?
Path: [Settings]-->[About PadFone]-->Build number
Example: You should be able to see the build number JP_PadFone-11.X.X.X, where “JP” means SKU.
PS: Due to this Android 4.4 upgrade would reset your device, please do refer the upgrade SOP to backup your personal data.
So, yeah, be sure to follow ASUS' directions carefully and only flash from the correct software version. The update weighs in at over 900MB, so you may want to wait for an unmetered connection as well.
Source: ASUStek Support