With Samsung and HTC revealing all, Sony is one of the companies that's yet to reveal an update to its flagship handset.
The Xperia Z1 and its 20.7-megapixel camera, side power button and waterproof OmniBalance design graced us with its presence in September 2013. A slightly more rounded version of that handset appeared in the form of the Xperia Z2 in February 2014, followed by the beautiful and more refined Xperia Z3 that won over hearts in September 2014.
However, if you thought the Xperia Z3 was the one, it might be an idea to hold off on the wedding plans for now, because rumours of the Xperia Z4 have been churning for months. We've rounded up all the rumours and speculation so you can see what might arrive and as usual, we will update this feature as more is unveiled.
Sony Xperia Z4 release date
CES and MWC came and went with no sign of the Sony Xperia Z4, but we did get the Sony Xperia Z4 Tablet, so this latest Xperia generation has started, just not at the smartphone end of the line.
Sony's next traditional launch event is IFA, held in Berlin in September, which could be the obvious launch venue for this new device. That will give Samsung, HTC, LG and others plenty of time to establish themselves before Sony Mobile has a competitor on the market. Will Sony wait that long? We're not sure they will.
The most recent rumour comes from serial leakster @vizileaks who claims Sony's next smartphone release will go by the name of the Xperia Z3 Neo instead of Xperia Z4. This suggests the rumours in this feature refer to a slightly upgraded device rather than a brand new flagship, which if true means it's possible we may end up seeing two new Sony smartphones before the end of the year. As the leak can't be verified however, we will continue to use Xperia Z4 when referring to the rumours below.
Sony Xperia Z4 design
According to an unnamed source of Android Origin, the Sony Xperia Z4 will come with Qi wireless charging support, which will mean ditching the magnetic charging port that arrived on the original Z. The source also claimed the flaps covering the Micro-USB port will be removed for the next Xperia Z device but the waterproofing rating will remain the same as the Xperia Z3, at IP68.
With Sony's launch of the Xperia M4 Aqua, the side charging port is gone and the Micro-USB is now proofed, so we'd fully expect that to be the case for the Xperia Z4. That should lead to a slicker design.
A leaked screen frame claiming to be of the Xperia Z4 from Future Supplier suggested a narrowed bezel, a position move for the front speakers and a switch of places between the proximity sensor and the front-facing snapper. Fleshing everything out is a set of Xperia Z4 images from @onleaks that claim to be for internal Sony use, but give us a good idea of how the Z4 might look.
Phone Arena also claims the Xperia Z4 will be more rounded in terms of shape than its predecessor, as well as see a reduction in the top and bottom bezels.
More recently, three hands-on images claiming to be of the Xperia Z4 were posted by Greek website In2Mobile. It's difficult to tell how legitimate the images are however, as they have a close resemblance to the Xperia Z3, especially the image of the rear snapper.
This could mean that the Xperia Z4 is set to remain very similar in terms of design to the Z3, or it could just mean the images are just of the Xperia Z3. There is a mysterious model number - E6553 - in one shot however, which has been associated with the Xperia Z4 in previous leaks so it's possible the images are real but we can't be sure for now.
Sony Xperia Z4 display
The Xperia Z1 launched with a 1920 x 1080 display in September 2013 and while Sony's competitors started opting for QHD displays with some of their devices, Sony stuck to its guns launching the Xperia Z3 with the same Full HD display.
Rumour has it this might change for the Xperia Z4 however. Some claims suggest Sony will release two variants of the new flagship, a Quad HD model and a 1080p variant. Whether they will both be available everywhere in the world isn't clear but apparently the US will be getting the QHD model. The same source, Chinese site ePrice, suggests the handset will come with a 5.2-inch display.
Supporting the 5.2-inch rumour more recently are several images of an LCD digitiser that appeared on the Esato forum, with user Tizzo claiming they were of the Xperia Z4. The user also said an undisclosed LCD display supplier had confirmed the 5.2-inch size, along with a QHD resolution.
A 5.2-inch display, matching the Z3, fits with some leaked chassis images. These fit the design rumours, but also sit very close in size to the Xperia Z3. Looking at these images, it seems a good bet that the Xperia Z4 display will be 5.2 inches.
Sony Xperia Z4 camera
Sony's 20.7-megapixel rear camera has been the focus of the marketing behind the Xperia Z1, Z2 and Z3, with the megapixel count surpassing many other flagship smartphones on the market.
GSM Arena's source claims we could see an improvement on the rear camera of the Xperia Z4 but rather than increase the number of megapixels, the source claims there will be a new curved rear sensor instead. There have also been rumours of two more lens elements that are said to collect more light.
Phone Arena has reported that the front-facing camera will see a bump in resolution too, with a 4.8-megapixel snapper with wide-angle view suggested. Sony also has recently announced the IMX230 sensor, offering a 20.7-megapixel resolution, image plane detection autofocus technology, real-time HDR stills and 192-point autofocus for blur-free images. Hopefully that will be making its way onto the Xperia Z4.
The company claims the IMX230 will be the first CMOS sensor for smartphones that has the ability to track fast-moving subjects and it will also support 4K video.
There have been other leaks to suggest the Xperia Z4 will arrive with an IMX189AEG CMOS image sensor, which is the first high-speed and high-sensitvity CMOS image sensor with active colour sampling. According to Chinese website CNBeta, the sensor will be able to record 2K video at 16,000fps and 4K at 240fps, which would be much faster than the Xperia Z3. Whichever sensor Sony opts for, it looks like the Xperia Z4 will continue with the camera focus.
Sony Xperia Z4 hardware
In terms of the hardware, the Xperia Z4 is rumoured to be arriving with a Qualcomm Snapdragon 810 2.8GHz octa-core CPU under the hood.
There is also said to be 4GB of RAM coming, which is 1GB more than the Xperia Z3 and the minimum internal storage capacity is said to be starting at 32GB for the Xperia Z4, rather than the 16GB of the Xperia Z3.
When it comes to the battery, the Xperia Z4 is rumoured to sport a 3420mAh capacity, which whacks an extra 320mAh compared to the Xperia Z3's battery so if this rumour is true, you should get some serious juice out of the new device. The Z3 was a good performer on the battery and any increase in capacity would be popular.
The rumours surrounding the Xperia Z4 are in full swing and many make perfect sense - especially those relating to the open Micro-USB in the light of Sony's recent launches.
We can't be sure that Sony will increase the resolution of the display. Looking at recent rival launches, the Samsung Galaxy S6 is QHD and LG has also confirmed its yet-to-be-announced LG G4 will also offer a QHD display but the HTC One M9 remained at Full HD. We'd be surprised if the Sony Xperia Z4 didn't have the Qualcomm Snapdragon 810 chipset however.
The timing is still an unknown, but we'd expect a device that looks a lot like the handset it replaces. We'd also expect it to launch at the same price, around £579.