Windows Phone developers can now download WP8 Update 3
If you are a developer of Windows Phone apps, you can update your Windows Phone 8 device to the announced OS update titled “Update 3” or “GDR 3” now.
Requirements are that you (a) have an active Windows Phone Dev Center account; OR (b) have an active App Studio account; OR (c) be running a registered developer device (‘dev unlocked’ phone)
Note that You CANNOT REVERT to a previous OS version once you have taken an update via this program.
The tool itself is very simple, allowing you to opt-in or -out of pre-releases of the Phone OS with one click.
The download is available here: http://www.windowsphone.com/en-us/store/app/preview-for-developers/178ac8a1-6519-4a0b-960c-038393741e96