Google hopes the price cut encourages more developers to buy the Pixel C tablet to test Android apps.
To be eligible for the discount, you must go through Google's special developer webpage, but as Arstechnica notes, it looks like Google is selling the tablet to anyone. The price cut includes the tablet only, as an attachable keyboard is an extra $149.
If you're looking to fiddle around with the latest version of Android, you may want to take advantage of this deal. It's not clear how long Google will be running it.