Currently Sony Xperia Z is not even launched and company has released its kernel source code for download. Phone is going on sale in late february or march, it was announced at the CES 2013. With the use of Source Code, developers develop custom ROMs for the device.
If you are developer and need the source code than read out details first. Sony Xperia Z source code weighs in at 203MB, and can be found at the Sony open-source archive linked below. Its software version is 10.1.D.0.317.
By Releasing code before release, Sony is setting a good example of what what an OEM should do, and hopefully other companies will follow its lead.
Additionally, Sony Xperia Z is powered by a 1.5GHz Qualcomm Snapdragon S4 Pro quad-core processor, a 5-inch Full HD display, 16GB built-in memory with a microSD card slot for expandable storage. Device is fueled up with 2GB of RAM, 13MP rear-facing camera, 2.2MP front-facing camera, 2,330 mAh battery, and will be running on Android 4.1 Jelly Bean.
Checkout Sony Xperia Z portal for its availability in different regions and other news.
Source: Sony Mobile Developer