I was curious about this too. I did a lot of research in preparing for STS by using the search feature available to answer my questions in regards to the program.
Yes, Cathe put the recovery week as week 9 in the rotation, HOWEVER when it came up again in another thread Cathe stated the recovery week is actually to be taken
every 4 weeks. Trust me, your body will thank you for it! I just finished Meso 1 and I am happy to have the recovery week for a physical and mental rest. I am doing "easy" steady state cardio and yoga/stretching.
Do what works best for you, maybe decide as you approach the week 4 mark and see how you feel. For Meso 1 you may just be able to go straight through for the 8 weeks, but when you really start lifting heavy in Mesos 2 & 3, you may want to consider the break in between as well as after each meso.
Also, Cathe said about just doing Meso 3 for 4 weeks and only do 8 weeks of the other 2 Mesos. So, I wasn't sure what your plans were for Meso 3, just thought I would pass that along.
If I come across that thread again, I will post it.
Good luck! I chose the 3.5 month rotation as I was excited to get through STS for the first time. I am already planning to do STS again as I am seeing strength gains faster than I ever have and I'll either do a 6.5 rotation or a pyrimid rotation (M1, M2, M3, M2, M1).
Gina