The new headset builds integrated eye tracking into the Vive Pro, making foveated rendering a built-in experience rather than a pricey add-on. Foveated rendering uses eye tracking to increase the quality of the image where you're looking.
Hands on: HTC Vive Pro Eye review
The things you're not looking at are in less quality, which allows your PC to devote all its graphical power to increase the detail in what you're looking at.
The Vive Pro Eye also gets a slightly tweaked design, with its two cameras on the outside of the device getting a light blue highlight - making it look like the Vive Pro has eyes. Other than that, the Vive Pro Eye has all the same specs that the Vive Pro does. Dan O'Brien, HTC Vive's GM of Americas, says the Vive Pro Eye came about because developers were asking to do more.
Elsewhere, HTC is upping its software efforts. It's got a Netflix and Xbox Game Pass like service called Viveport Infinity launching on 5 April (that's Vive's birthday). You'll have access to hundreds of games for one subscription fee. It won't just be locked to Vive headsets though, you can also use it for Oculus Rift and other third-party headsets.
The Vive Pro Eye will launch in the second quarter of 2019, but there's no word yet on how much it could cost or where it'll ship. Viveport Infinity will launch 5 April - no word on price there either.