Sony's device naming scheme for Xperia phones has been confusing for years. The 'XZ' line of phones serve as the company's mainstream devices (akin to a Galaxy S device), with the 'XZ Premium' phones being ultra-flagships (like a Galaxy Note or LG V phone). On top of that, there are budget devices under several monikers, like the L2, R1, and XA2.
It looks like Sony might be switching up its naming scheme, according to information obtained by Evan Blass (@evleaks on Twitter). He posted an image of Sony's next flagship phone and claims it will be named 'Xperia 1.' The device was previously expected to be called the Xperia XZ4, so this could be the start of Sony introducing a simpler naming convention.
Previous rumors and renders point to the phone having a 21:9 screen, a Snapdragon 855 processor, 6GB of RAM, a 4,400mAh battery, 128GB of internal storage, and Android 9 Pie. Evan Blass also revealed the phone will have a 4K HDR OLED screen, meaning this is likely a successor to the XZ Premium line (which has had 4K screens for a few years).
Sony already teased the release of a 21:9 smartphone for Mobile World Congress next week, so it probably won't be long until the phone becomes official.