The Sony Xperia Z4 has been unveiled in Japan, but according to reports, the rest of the world would have to wait for a different flagship phone from Sony, rumored to be coming in May.

GSM Arena wrote that the Z4 will "remain as an exclusive for its homeland."

"Instead Sony will be premiering a proper flagship smartphone later this year, supposedly this May," the same report added.

Sony has not confirmed this rumor so it's best to take this piece of information with a pinch of salt.

As for the improvements in Xperia Z4, Forbes said that the difference is just small compared to the Xperia Z3 released in September last year.

"Sony has continued with its partial-improvement policy of making minor changes to its main-line of smartphones with the Z4, save for the new Snapdragon 810 processor," Forbes added.

The new phone reportedly has the same shape and design as other previous releases, though it weighs lighter compared to the Z3.

"It has the same 5.2-inch 1080p IPS LCD display, 3GB of RAM, MicroSD, waterproof housing and 20.7MP rear camera. The front camera, however, has been upgraded to a 5.5MP sensor with a 25mm wide-angle lens (same as the rear) and image stabilization," explained Forbes.

In a similar report, The Verge said the phone is 6.9 mm-thick with a 144g metal and glass body.

"The phone runs Android 5.0 Lollipop and is water- and dust-resistant. Unlike the Z3, no smaller 'Compact' edition has been announced," noted The Verge.

Its battery is also reportedly smaller, with 2930mAh if it will be compared to the 3100mAh power pack of the Z3.

Meanwhile, GSM Arena said that a "resolution bump" might be seen on Sony's next flagship as it promised to improve user experience through hardware upgrades.

Z4 delayed in U.S.?

It's still uncertain if Sony will be releasing a new flagship phone or if the Xperia Z4's international release will just be delayed. Previous rumors claimed that the U.S. market may be getting the device in summer.

Quoting a Sony spokesperson, Forbes said Sony mobile is "considering the feasibility in other markets." However, the limited release and quiet launch in Japan recently has got people thinking if Sony will soon close its smartphone program.

According to Forbes, Sony's effort in the market has been brushed off by competitors like Apple and Samsung.

"Android devices has led some to speculate that Sony might pull-out in the near future. Sony had said previously that it will focus on more profitable areas of its business - namely camera sensors and gaming - and would 'no longer pursue sales growth in areas such as smartphones,'" added Forbes.

What do you think? Will Sony release the Z4 in summer or will it unveil a totally different flagship phone in May?