The next alpha for Drupal 8 will be alpha 14! Here is the schedule for the alpha release.

August 3rd-5th
Only critical and major patches committed
August 6th, 2014
Drupal 8.0.0-alpha14 released. Emergency commits only.

(Note that there are two concurrent Drupal 8 sprints Aug. 7-10, so we aren't planning to have the usual "disruptive patch window" following this alpha.)