There may be 11 participants in the next 10 person Republican debate, based on new rules announced by CNN today. 

Originally, CNN said that only candidates in the top 10 from polls taken from July 16 to September 10 could particpate. While similar to the Fox News approach for the first debate, it failed to account for shifts in public opinion occurring as a result of that event.

Fiorina participated in an earlier forum at the August 6 Fox debate, and her strong performance has propelled her to well within the top 10 in polls taken since then.

The new CNN rules will keep the original criteria, while adding a separate criteria to include those in the top 10 for polls taken post-debate until September 10.

This likely means 11 participants at the September 16 debate, including the 10 candidates from the first debate plus Fiorina. As it turns out, this appears to be a good break point, based on the average of the most recent polls: 

Here's the full CNN statement on the rules change. The debate will take place at the Reagan Presidential Library.