Even before the calendar made its annual turn, four Android flagship smartphones are already expected to battle their way in 2015. Two of them -- the Samsung Galaxy S6 and HTC One M9 -- have been revealed, while the other two are expected to arrive at later dates.

These remaining handsets are the LG G4 and Sony Xperia Z4. The former, as previously reported, may already arrive the soonest next week, if speculations are to be believed.

However, with the Xperia Z4, rumors tend to be rather displeasing. For one, it's believed to be the last of Sony's smartphones. If the company goes by the saying "save the best for last," prospects will have to expect a beast.

According to the PCAdvisor, signs have pointed that the handset is being delayed rather than cancelled. The outlet cited rumors, which claimed that the Xperia Z4 has appeared in January's International Consumer Electronic Show -- though only in closed doors.

A "trusted source" has told the PCAdvisor that Sony's next flagship won't arrive until September, and this looks to be a launch in the Berlin-based IFA. The event takes place on Sept. 4 to 9, the outlet said.

As we wait for official word, here are five of the most interesting specs and features pegged to pack in the Xperia Z4:

1. Display

A new report has suggested that the Xperia Z4 will own a 5.2-inch 1080p display, Know Your Mobile noted. This information follows rumors pointing to a 5.4-inch Quad HD Triluminos display.

If this holds truth, the new Xperia will not be much different from its predecessor, which measured the same, full HD screen.

2. Processor

This may not be surprising as Snapdragon 810 already appeared since the LG G Flex 2. However, such processor certainly puts the Xperia Z4 to the A-list of 2015 smartphones it seeks to deserve.

Alongside the chip, 3 GB of RAM is expected to power the device, TechRadar pointed.

3. Measurement

The Xperia Z4 is pegged to measure 146.3 x 71.9 x 7.2 mm, Android Pit cited. If this bears truth, the device looks to sport very little difference from the Xperia Z3, which comes at 146 x 72 x 7.3 mm.

4. Camera

As told by Trusted Reviews, the Xperia Z4 could introduce a new lens, though it may still pack its predecessor's 20.7 MP snapper.

5. Storage

As previously reported, the Xperia Z4 has been tipped to allot a single port flap, speculated to give room for nano SIM or a microSD card. A mysterious-looking port was also spotted in recent leaks.

The Xperia Z4 is speculated to sell for $1,250. For more information about the current Xperia Z3, head over here.

Check out stunning Xperia Z4 concepts here, here and here.