Tamron 28-75mm f/2.8 Di III VXD G2 Lens for Sony E Mount with Altura Photo Advanced Accessory and Travel Bundle

Q: Does it compatible with a6400?

Yes, this lens works fine on the A6400. I have an A6100 and have used it a time or two. You just have to remember there is a crop factor due the the size of your sensor. So the 28-75 will actually be around 40-105mm. So you loose the medium wide angle on the front side of the lens. Still a good range though