You can sign 28, but you can only bring in 25. Now, in Auburn's case, we only brought in 20 scholarship players last year, so therefore we have room for 5 prospects to count towards last year's class, provided that they graduate from HS early and are qualified to enroll early.
As of right now, Auburn has two prospects that are definitely going to be able to enroll early (Jessel Curry and Craig Sanders) so those two will count towards last year's class. There might be one or two more that'll be able to enroll early. There are probably one or two prospects that won't be able to qualify and will be sent to either JUCO or Prep. So, lets say that 3 prospects enroll early and 2 prospects won't be able to qualify, that would mean that Auburn will be able to sign 30 and bring in 28 new prospects.
So, to answer your question, Auburn is expected to bring in a stocked class.