Soon after the iOS 9 Gold Master (GM) version became available, popular jailbreak developer iH8sn0w, whose real name is Steven De Franco, successfully jailbroke the new iOS iteration running iPhone 5. iH8sn0w - the creator of sn0wbreeze, p0sixspwn, iFaith and other jailbreak tools - posted a video demonstrating the jailbreak with Verbose, custom boot logo, code injection and Cydia.
The video shows the iPhone running on build 13A340, the same build number for the GM version Apple made available for developers via the Apple Developer site. Here is what iH8sn0w says about the iOS 9 jailbreak.
"Poking into iOS 9 is fun. A little annoyed at some new things. But very surprised at how similar it is to iOS 8 internally.
Worth noting, iOS 9+ arm64 iDevices now enforce a checksum on __TEXT/DATA.const regions of the kernel through the use of TrustZone. Modifying said sections will cause the device to panic (either at kernel or EL3 will force a reboot if the kernel refused to gracefully panic). Essentially, it's KPP (Kernel Patch Protection). You can race it though if you want to play with things. Just be quick! ;P
Also, there should technically now be two additional partitions (baseband_data [s1s3] and logs [s1s4]) but didn't really bother with those as they weren't critical."
We might get to see more jailbreaks after the rollout of iOS 9, but iH8sn0w has come up with this jailbreak even before the OS's public release, despite Apple patching two exploits in iOS 9 beta 5, as confirmed by the Pangu team recently. If you have any doubts about the jailbreak, check out the following video.