There's a slight change in its design compared to the Mi Band 3. Gone is the recessed button, which is replaced by a circular halo touch-sensitive button. There is also a change in the Mi Band 4's charging cradle, which now covers the whole body rather than being attached at one end of the sensor unit.
The Mi Band 4 will have improved heart rate monitoring and come with Xiaomi's AI voice assistant - Xiao AI, making it the first Mi Band device to do so.
As with all previous Mi Band updates, the fourth generation would bring new features while honouring the low price of its predecessors. So it looks like we can look forward to a cutting-edge fitness tracker that keeps that price tag reasonable. More details will be updated soon: https://gearvita.com/xiaomi-mi-band-4.html