http://www.techradar.com/news/tiny-samsung-galaxy-s9-mini-could-be-in-the-works

Other than the iPhone 8, Sony Xperia XZ1 Compact and their predecessors there haven’t been many high-end compact phones in recent years, but Samsung could be about to add to the list with a Samsung Galaxy S9 Mini.

Known leaker I ice universe has said as much on Weibo (a Chinese microblogging site), adding that the screen is less than 5 inches and that it has a "full screen", which suggests that it will have minimal bezels and a super-widescreen 18.5:9 aspect ratio, just like the Samsung Galaxy S8 range.