We only got the Sony Xperia Z3+ recently, but already the Sony Xperia Z5 has been announced and with a new number there's an expectation that it will be a significant upgrade.
While not everything has changed in Sony's latest the addition of a fingerprint scanner alongside an improved camera and a hefty amount of power should keep fans happy. But it is enough for the Xperia Z5 to go toe-to-toe with smartphone heavyweights like the Samsung Galaxy S6 and iPhone 6?
With a slim 7.3mm thick metal frame and a frosted glass back the Sony Xperia Z5 doesn't stray far from the form factor of previous Sony flagships, but the power button on the side has been slightly redesigned to incorporate a fingerprint scanner.
That's a first for Sony and its set to support online payments, as well as being a speedy way to unlock the handset.
Like the Xperia Z3+ the Sony Xperia Z5 is also IP68 certified dust and water resistant, with a capless microUSB port, so you don't have to fiddle with a flap every time you want to charge the phone.
It's a premium if slightly overfamiliar design, finished off with a choice of either plain black or white colours or more adventurous gold or green options.
Samsung completely changed things up for the Galaxy S6, but in doing so created a handset which looks a bit like a cross between the iPhone 6 and the Sony Xperia Z5. It has a sleek 6.8mm thick metal frame and a glass back, but the corners are more curved than on Sony's phone and the back isn't frosted.
Like the Sony Xperia Z5 it has a fingerprint scanner, but this time below the screen and unlike Sony's handset it's not dust or water resistant.
The iPhone 6 has a similarly rounded shape to the Samsung Galaxy S6 and also has a fingerprint scanner beneath the screen. It's almost as slim too at 6.9mm thick, but unlike Samsung and Sony's flagships it has a metal unibody. It's a great design, but all three handsets look distinctly premium.
The Sony Xperia Z5 has a 5.2-inch 1080 x 1920 IPS display with a pixel density of 428 pixels per inch. An anti-fingerprint coating should keep it smudge-free and it's designed with good contrast and vibrant colours in mind.
The Samsung Galaxy S6 might have it beat though, with its 5.1-inch 1440 x 2560 Super AMOLED screen, giving it a pixel density of 577 pixels per inch. Not only is it incredibly sharp, but it sports bright, vivid colours and good outdoor visibility.
The iPhone 6 has the smallest and lowest resolution screen of the three, with a 4.7-inch 750 x 1334 display for a pixel density of 326 pixels per inch. But while it's a shame it's not sharper, the display on the iPhone 6 still offers brilliant contrast and colour reproduction.
Power and performance
There's an octa-core Snapdragon 810 processor and 3GB of RAM at the heart of the Sony Xperia Z5. That's the same as the Xperia Z3+, but we found performance with that phone was generally smooth, so it's not too much of a worry, though the Z3+ did sometimes heat up.
The Samsung Galaxy S6 has an octa-core Exynos 7420 processor plus 3GB of RAM, which also delivers silky smooth performance for the most part, though waking up the phone from sleep can noticeably take a second or two.
On paper the iPhone 6 is the least powerful of the three, as it has just a dual-core Apple A8 processor and 1GB of RAM, yet as with its rivals it offers generally slick performance in day to day use.
Sony has done a lot of work on its smartphone snapper, equipping the Xperia Z5 with a new 23MP sensor. Low light photography is supposedly better than it's ever been in a Sony phone, while autofocus happens in just 0.3 seconds, which Sony claims is faster than any other smartphone.
The snapper also supports 5x clear zoom with minimal loss of quality and can shoot video in 4K, using an improved version of Sony's SteadyShot technology for blur-free footage.
The front-facing camera meanwhile is a 5MP one with a 25mm wide-angle lens, so you can fit lots in the frame and it has the same SteadyShot technology as the main snapper.
That all sounds impressive, but the Samsung Galaxy S6 has one of the best smartphone cameras we've ever come across. Its 16MP sensor is highly capable in both bright and low light and while you can easily point and shoot there's also a strong selection of manual controls.
Like the Sony Xperia Z5 it supports 4K video and with optical image stabilisation you can be confident that your photos and footage will come out smooth. Round the front it has a 5MP snapper too and just like the Z5 it can take wide-angle shots.
The iPhone 6 has a pretty great camera as well. It's only 8MP but it can take impressive photos, helped in part by 'Focus Pixels', which lead to faster autofocus and improved clarity.
It's a strong snapper, with simple, intuitive controls and it's good for video too, supporting slow-motion footage at up to 240fps, though the front-facing camera is just 1.2MP.
OS and features
Both the Sony Xperia Z5 and the Samsung Galaxy S6 run Android 5.1, but the overlays are different and include a handful of special apps and features. The Xperia Z5 for example supports PS4 Remote Play and High-Res lossless audio, with lower quality tracks upscaled to near High-Res quality.
The Samsung Galaxy S6 meanwhile has a heartrate monitor and a Smart Manager app, which shows you the security of your phone, battery life, RAM use and storage all in one place.
The iPhone 6 is the odd one out here as it runs a completely different operating system. With iOS 8 on board you get access to Apple's rich app ecosystem at the cost of some of the customisation and freedom you get on Android. Like Samsung Apple has also gone big on health and fitness, equipping the iPhone 6 with an M8 co-processor, tasked purely with keeping track of movement.
The Sony Xperia Z5 has a 2900mAh battery, which can supposedly last for up to 2 days of use, with a STAMINA mode keeping it going even longer. It also supports Quick Charge 2.0, so you can theoretically get up to 5.5 hours of usage from a 10 minute charge.
The 2550mAh juice pack in the Samsung Galaxy S6 supports fast charging as well, plus it even supports both wireless charging standards, but you're not going to get anywhere near 2 days out of it. You should get a full working day from it, but not much more.
The iPhone 6 has just an 1810mAh battery but it can keep on chugging for a full day of moderate use. That still leaves it well behind what the Xperia Z5 promises though.
Price and availability
The Sony Xperia Z5 will be hitting stores in October and while no pricing has yet been confirmed we'd expect it will have a premium RRP of perhaps around £500/$650/AU$1000.
The Samsung Galaxy S6 has an RRP of £559/$599/AU$999, while the iPhone 6 starts at £539/$649/AU$999, so they're all expensive, but you don't have to wait to buy an S6 or an iPhone 6, as both are available now.
The Sony Xperia Z5 doesn't seem like a massive change from the Xperia Z3+, but with a fingerprint scanner and a new camera it could still be a worthy upgrade.
Those features, combined with its powerful innards, supposedly long-lasting battery and water resistant design should make it a capable flagship. We can't say for sure until we've put it through its paces, but on paper the Sony Xperia Z5 looks to be a worthy rival to both the Samsung Galaxy S6 and the iPhone 6S.