From this thread by @batrak http://www.vexiqforum.com/forum/main-category/official-answers-ask-the-vex-staff/30229-max-programs-on-brain
…it depends!
Modkit is 4 as there are specifically 4 slots. In ROBOTC, it is more to do with the size of the files rather than the number. I’m not sure what the memory allocated to this is, but you can store a lot more than 4 normal VEX IQ programs this way.