I believe there are 2 at-large bids, and BYU should get one unless OSU is upset.
I don't think that changed this year. Big West adds volleyball next year, right?
Through the 2013 tournament, each of the three major conferences (MPSF, MIVA and EIVA) received an automatic bid to the Final Four, with one additional at-large bid. The remaining bid was an at-large bid that could be awarded to any team in Division I or II (including Rutgers–Newark). Generally, the best team not receiving an automatic bid (usually from one of the three major conferences) received the at-large bid.
Beginning with the 2014 championship, the field expanded to six teams, with the two new teams being the champion of Conference Carolinas and one extra at-large entry.