It is preliminary and is not available on the installation media.
It is highly recommended to upgrade - to create a backup in Time Machine.
Release install at your own risk.
Year of release: 21 July 2016
Version: 10.12 Public Beta 2
Developer: Apple Inc
Platform: Intel only
Language: Multilingual.
Tablet: Not required
Requirements:
Installed MacOS Sierra 10.12 Public Beta
Supported models:
* iMac (mid-2009 model or newer)
* MacBook Air (late 2010 model or newer)
* MacBook (late 2009 model or newer)
* Mac mini (early 2010 model or newer)
* MacBook Pro (early 2010 model or newer)
* Mac Pro (early 2010 model year or newer)
http://rapidgator.net/file/f0aeb09e57034ce96eb7cbabb1bdc079/MacOS.Sierra.10.12.Public.Beta.2.Update.part1.rar.html
http://rapidgator.net/file/eca1f370daf453bd031f9404d9fa3038/MacOS.Sierra.10.12.Public.Beta.2.Update.part2.rar.html