The offer is only valid for the purchase of a single tablet, and is only being extended to US-based developers. To qualify for the discount, registered developers have to sign up to receive a unique code to purchase the Pixel C, which will be emailed to valid accounts.
With the announcement of Android N developer builds, Google just got serious about tablets. The builds of Android N include Split Screen support for apps, fixing one of the criticisms found in reviews of the recently released Pixel C. The restriction of the discount to US-based developers is frustrating for developers in other countries, but it is what it is.
We hope we’ll see some sort of discount extended to developers outside of the US, but we’ll have to wait and see.