Sony Xperia Z1 was released in September 2013. Xperia Z1 is powered by a Qualcomm Snapdragon 800 2.2GHz quad-core processor, and 2GB of RAM. The 5″ TFT display has a resolution of 1920 x 1080 and is manufactured utlising Sony’s Bravia technology. Internal storage comes in at 16GB, with a further 64GB available with microSD. Z1 has a 20.7MP sensor, Sony’s in-house G lens and image processing algorithms, called BIONZ.
Sony Xperia Z1 has not received official Android 5.1.1 yet. However using CM 12.1 ROM, it is possible to update Xperia Z1 to official Android 5.1.1. Besides this, you will get more features and better performance than the stock ROM. Follow the guide below.