The Xperia XZ1 was originally announced at IFA 2017, and it arrived in the United States in September. The original price was a whopping $699.99, but as usual, the price started to fall shortly after launch. The XZ1 dropped to $599 back in November, and now you can get the 'Warm Silver' model for $543.44 from Amazon.
If you're not familiar with the XZ1, it has a 5.2" 1080p IPS display, a Snapdragon 835, 4GB of RAM, 64GB of storage, a 19MP rear-facing camera, a 13MP front-facing camera, and a 2700mAh battery. It was the first phone to ship with Android 8.0 Oreo, since the Pixel 2 hadn't been officially announced at that point.
It's worth noting that the US version of this phone does not have a working fingerprint sensor - you'll need to flash the EU firmware for that. Also, Sony is expected to announce the XZ2 at the Mobile World Congress next month, but that phone will likely be much more expensive (at least in the US). You can find the XZ1 at the source link below.