Apple has just released the fourth beta of iOS 9.1 which is now available to registered developers or those who installed one of the previous betas. You can already do this the update from the settings of the iPhone and then retrieve the firmware from the portal developers.
The weight of the update with the build 13B136 is huge with 16 GB (iPhone 6s Plus) against 277 MB with beta 3. Either there is a concern, there is a lot of changes. For now, Apple did not specify what changes but we’ll get if we spot things evidence.
If you are enrolled in the beta testers of the program, you can download the public beta of iOS 9.1. You can register now if not already at apple website.
Note: the download can take several hours, 3 hours with us, because of the large number of simultaneous downloads in … Apple servers now.