Microsoft has revealed through Major Nelson's Blog
that a Preview Program will be coming to the Xbox 360. Undoubtedly, Microsoft has found the user feedback from the Xbox One's Preview Program to be of great assistance in making the console meet consumer needs and has decided to expand the program to their previous console.
In order to be a part of the Preview Program, you'll need to receive an invite that will come by way of an Xbox LIVE message to your console. If you receive one, simply head to settings, and then select account management, where you should see an option called "Xbox 360 Preview Registration". Sign up there to enroll your console. You won't receive any updates immediately, but as they're ready to be rolled out, you'll be notified that an update is coming.
In the first Preview Program update, preview members will be able to test new features, including improvements the ability to troubleshoot common network issues from the 360 and a new Network Connectivity test that also checks for Download and Upload speeds. Further changes are promised to arrive later in the year.
Invites for the Preview Program have already begun to roll out. At the moment, this appears to be invite only, though if there are other ways to sign on, we'll let you know!