No, you do not have to have completed any 100s to
enter Tevis. For this year, you do need to have completed at least 150 miles of
sanctioned rides, with the rides having been at least 50 miles in length. I've
heard that next year the prerequisite will be 300 miles of rides.
The intent is good, unfortunately, it doesn't make any allowances for the person
who has ridden for many years, has miles & miles of conditioning rides under
their belt, yet doesn't participate in sanctioned rides. And, at the
opposite end of the spectrum, it allows people who have very little
experience to do a few 50's one year, then enter Tevis. Which rider is more
qualified? On the other hand, the trail can get to anyone and their horse,
regardless of their qualifications, so I don't know that any prerequisite will
make the ride any safer for those participating.