It's kind of a gray area....the T-38 has a set absorption capability it can maintain to still graduate students on time. Without diving too much into the specific numbers, at Vance right now there are X numbers of students taken from each class, and there are Y classes per fiscal year. So, X*Y=total number of students who will go through the T-38 syllabus at Vance in FY18. Of that #, so many of the slots have been sold to Saudi, Iraq, Kenya, etc. A few slots are also bought by the Guard & Reserve, with the rest being Active Duty slots up for competition. Those international/guard/reserve slots are somewhat equally dispersed between those Y classes by AFPC. Due to students rolling back into later classes due to deficiencies/medical/emergency leave/etc, there are sometimes a disproportionate number of slots spoken for in that class when track select comes along. So, while they aren't "taken" from Active Duty, there is an element of luck and timing present as to how many spots we can compete for. To answer your other question, yes those students are guaranteed their T-38 no matter what their MASS in T-6s is, as long as they are able to pass the T-6 syllabus.