How can you tell if you have a surface pro 4 or a surface pro?

First, you can check the device model in Control Panel > System. You can also check the box where the computer is previously stored and check the device model there. Aesthetically, the Surface Pro 4 and the new Surface Pro has nil to no differences. Another way to check your model is by finding the serial number on your device then contacting Microsoft. Lastly, you can compare technical specifications. Attached is a photo of technical specifications comparing the Surface Pro 4 and the new Surface Pro.