The A9 smartphone itself is in line with the One family's premium build, featuring an all-metal unibody, but a slimmer, lighter design.
The A9 has a 5in AMOLED screen with a Full HD resolution, with Qualcomm's octa-core Snapdragon processor and 2GB of RAM powering the smartphone. You can choose between 16 and 32GB versions, with the option of expanding the internal storage up to 2TB thanks to an SD card slot.
Read our HTC One A9 hands-on review
Instead of chasing smartphone specifications, HTC is focusing on giving users the best camera experience, with the main 13MP camera now equipped with Optical Image Stabilising to reduce shakiness.
Along with 4K videos, the A9 now supports RAW camera format. The front camera utilises HTC's UltraPixel sensor to reportedly capture 300 per cent more light than rival smartphones. The camera app has also been redesigned with a simpler interface that splits normal camera, selfie and Pro modes.
Another new feature is Hyperlapse: the ability to speed up new or existing videos up to 12 times to create a time-lapse video. While Apple owners already have this feature thanks to Instagram's Hyperlapse app (which is still unavailable on the Google Play Store) HTC has a scoop with offering the feature built into the new A9.
More after the break
For those that use a smartphone as their main music source, you'll be pleased to hear that HTC will continue to support files up to 24-bit/192kHz resolution on the A9, with tweaks to the internal DAC, amplifier and 3.5mm headphone port.
One glaring difference is that HTC's trademark front-facing BoomSound stereo speakers have been swapped to make room for a fingerprint sensor - the first time on an HTC smartphone - which will work in conjunction with Android's Google Pay feature.
The One A9 has a 2150mAh battery and new power-saving features such as Doze and App Standby. HTC claims you should be able to watch 12 hours of HD video on a single charge.
Prices will vary according to your network provider, but is expected to be less than the flagship HTC One M9.
The HTC One A9 will be available in four finishes: carbon gray, opal silver, topaz gold and deep garnet, with the first three available in the UK from the beginning of November.
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