This is completely variable from program to program. Some don't need CS to start, others must have it.
MS4's should really know this because it can be potentially devastating, even more so since some medical schools don't require that CS be passed to graduate (just taken/attempted).
I think the interns and medical students need to actually get together and try and get CS completely eliminated for AMGs, though. It's a completely unnecessary exam given that the ACGME has to credential every single medical school, and it should be their job -- not the job of lay volunteers in 5 select cities -- to ensure that students receive adequate clinical training. Plus the fact that this exam costs over $1K and takes 2-3 months to receive the results is simply unacceptable, especially given the elusiveness of the exam criteria and grading. Add to that a passing rate of 94-98% for AMGs and you have a completely unfounded exam.