A few weeks ago, Google published preview builds of Android N, and they announced a developer discount page for the Pixel C. At the time, it was US-only and applied to the 64GB version, bringing it down to $450 USD. The website also seemed… broken… so I wasn't sure if Google were fixing it or whatever. A few people received discount codes on the first run, but the websites now say that they will email you within a few days with a promotional code.
The discount website has now been updated, and the terms have changed. The major difference is that it is now available in 13 countries: Australia, Austria, Belgium, Canada, France, Germany, Ireland, Netherlands, New Zealand, Spain, Switzerland, United Kingdom, and the United States, of course. The discount is now a blanket 25% off a Pixel C tablet (just one, like before). I haven't received the promotion code yet, so I can't confirm that it applies to both 32GB and 64GB models, but ZDNet claims it does, and Android Police states that Google confirmed it to them. The discount still does not apply to the keyboard.
Google's Nexus line has been known to limit API access, specifically by not shipping OpenCL drivers and pushing developers toward their proprietary RenderScript instead. That said, it should be kept up to date with Google's latest OSes for longer than most devices. Also, Vulkan is being considered a Google-supported API, so, unless something weird happens, Pixel C should get those drivers, which should be sufficient for upcoming GPU compute and gaming tasks.