The Sony Xperia series has been promised an update for Lollipop, and there is word that the Z4 will soon be announced, possibly as early as CES 2015 (January), or even Mobile World Congress (March 2015). There has been many rumors as far was what it will have, and this concerns the Xperia Z4 smartphone, the larger Z4 Ultra, the smaller Z4 compact, and even a possible Z4 Tablet.
Much of the rumors seem to agree that the Xperia Z4 will have a 5.2-inch display, and Phone Arena has stated that it will either have 1440p or 1080p resolution. There have been rumors of larger screens, such as Digital Trends supposition that it could go to 5.5 inches. It is estimated that the Z4 Compact will have a 4.7 screen with 1080p, while the Z4 Ultra will have a 6.44 inch with Quad HD (1440 x 2560) resolution. GSM Arena reports that there are rumors of a 13-inch Z4 tablet, which could have resolution as high as 3,840 x 2,400.
As for the camera, there are mixed rumors on that one. Tech Radar reports that it should have a 20.7 Megazpixel resolution on the rear, with a 4.8 Megapixel front-facing one. Phone Arena reports that Sony is working on a 16 Megapixel and 21 Megapixel Exmor RS IMX230 camera that enables blur-free tracking and snapping of fast-moving objects, and it suspects that this camera could end up on the Z4.
As for what is on the inside, Android Pit states that it will have a Qualcomm Snapdragon 805 processor, with Digital Trends hoping for the 64-bit Snapdragon 810. It will also have a Quad-core 2.7 GHz Krait 450 and 3GB of RAM. It should come as no surprise that will be loaded with Android 5.1 Lollipop.
Phone Arena also reports that the Z4 could have a unique interface, including Sony Small Apps multitasking suite, as well as possible control over Sony devices in one's household like the PS VITA, PS4, or TV set. As for the internal storage, it will be in 16 GB, 32 GB, 64 GB, and one estimate could be as high as 128 GB.
For the battery life, Tech Radar estimates that it will have a 3420 mAh battery, which is a step up from the 3100 mAh of the Xperia Z3.
This leaves only one rumor left: the release date. It would depend on when it was announced, but if Sony waited until MWC 2015, then the earliest that it would probably show would be in April.