873 Come Out for Day 1b
For comparison's sake, last year there were 1,297 runners on Day 1a, and 1,158 on Day 1b. The numbers went up considerably for the last two Day Ones last year, with nearly 2,000 on Day 1c, and more than 2,400 on Day 1d.
Sounds like today's total means that Burt Boutin has won himself a prop bet. The line for the bet was 940, and Boutin took the under.