A new firmware update with build number 14.4.A.0.157 has been certified by the PTCRB for the Sony Xperia Z1, Xperia Z1 Compact and Xperia Z Ultra. This appears to be a minor revision over the previous software that was certified, but never released, with build number 14.4.A.0.155.
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!]
Xperia Z1 build number 14.4.A.0.157 certified for C6902, C6903 and C6906 variants
Xperia Z Ultra build number 14.4.A.0.157 certified for C6802, C6833, C6843 and C6806 variants
Xperia Z1 Compact (D5503) build number 14.4.A.0.157 certified