Apple has released a second public beta for iOS 9.1, arriving as build 13B5119f to match the second developer beta.
Users who are participating in the iOS Public Beta program can find the iOS 9.1 beta 2 available now from the Software Update mechanism on their iPhone, iPad, or iPod touch through the Settings app. The delta update is about 170mb for an iPhone.
Anyone can choose to join the iOS Public Beta program by enrolling their device at the Apple beta testing website here. Because beta software tends to be buggy and less reliable than final versions, this is not recommended for most users.
iOS 9.1 is likely to focus on bug fixes and improvements to the operating system with few outward changes. Additionally, there are new emoji characters accessible in the iOS 9.1 keyboard, including a taco, a burrito, a piece of cheese, an eye rolling face, and a middle finger salute (important stuff, obviously). Some users have anecdotally reported the iOS 9.1 beta releases improve slow iOS 9 performance and helps to resolve battery issues, but currently there is no specific mention of this in the iOS 9.1 beta release notes.
While no timeline is known for iOS 9.1 to be finalized, the assumption is the release will debut alongside the iPad Pro and new Apple TV sometime in October. The most recent build of iOS for the general public is currently iOS 9.0.1.