You read that right, 6.4 inches. Xiaomi is likely to announce the smart-phone coming may 10th. The Chinese manufacturer is showing a teaser in its social network on Weibo. The biggest Smartphone thus far had a 5.7" screen.
The Weibo post shows that May 10th Xiaomi is hosting an even to introduce the Mi Max, or RedMi Max - in some of the GFXBench results a benchmark already appeared under that name with a full-hd-screen at 6.4". If the listing is right then the product will get a Qualcomm Snapdragon 650-soc, a hexacore with two Cortex A72-cores and four A53-cores. The memory would be 2GB with 16GB storage.
The smartphone is also listed having a 16Mpixels camera. Screens over 6" are rare, Huawei released a P8max just last year and I think Sony released an Xperia Z a couple of years ago with a 6.4" screen.