We will be introducing a new, hard cap of 600 members in a single guild for Cataclysm. This function will go live with patch 4.0.1 and is already live on the beta and PTR's.

As most of you already know, we have supported a soft cap of 500 members in a guild since World of Warcraft launched. We have allowed guilds to exceed the 500 limit up until now since being in a guild really just amounted to ranks and chat channels. With the advent of the new guild system in Cataclysm we are tracking many more things on each individual player in a guild and in order to support that, we need to limit the amount of members to a reasonable level.

The new cap of 600 members is fully supported in the new guild system and that means that everyone will be visible in the ui and able to contribute to all guild functions like experience and reputation gain. We have pulled a large number of statistics to get to the 600 member cap for guilds and we are happy to say that this value covers more than 99.9% of all the active guilds in World of Warcraft.

The small number of guilds that are over the 600 person cap will be able to keep their guilds intact (and fully supported in the new guild system), but they will not be able to add new members until they fall below the 600 member cap.