A new Windows Phone 8.1 update which takes the Windows Phone 8.1 developers preview version to 8.10.12400.899 from the earlier 8.10.12397.895 is rolling out now. The update though is not only limited to devices running developers preview but also is rolling out to devices like Lumia 630 and Lumia 930 which have shipped with Windows Phone 8.1.
Though the update may not bring big changes as it looks like a small jump in versions. So, it may mostly be a bug fixes and performance improvement kind of update. The update is 21 MB in size and takes 30-45 min in update installation.