If Sony does release this firmware it would replace build number 14.4.A.0.133 (which only hit selected carrier devices) or the older 14.4.A.0.108 that saw a global release.
Update: The generic Xperia Z1 Compact firmware is now rolling across the Nordics, Australia, Germany Middle East, US and Saudi Arabia. We would expect the Xperia Z1 and Xperia Z Ultra to follow shortly. [Thanks saeed !]
Update 2: The generic firmware is now hitting the Xperia Z1 (C6903) in Italy, Thailand, Singapore and the Philippines. The C6906 variant has seen the firmware roll to generic US handsets. Still no sign for Xperia Z Ultra users.
Update 3: French operator SFR has posted a changelog for this firmware which includes a more stable camera, improved battery life with Android Wear and patches for certain Google apps. [Thanks Francois!]