All devices with a screen width less than 768 pixels are eligible. There is a spike card in the current mobile web development iteration to investigate enabling it for tablets as well:
https://trello.com/c/VYQxLlqP/14-spike-1-hour-investigate-supporting-wikigrok-on-tablet

Kaldari

On Thu, Dec 11, 2014 at 5:35 PM, Erik Moeller <erik@wikimedia.org> wrote:
Congrats to getting this out, look forward to seeing the results!

Clarification question -- I recall this was intentionally limited to
smartphone scale viewport sizes so isn't easy to test on a desktop
device, is that still the case? If so could the exact test condition
for device eligibility be added to the wiki page?

Thanks,
Erik

--
Erik Möller
VP of Product & Strategy, Wikimedia Foundation