Major Nelson has announced signups for the 2013 Xbox Live Update for Xbox 360 Public Beta. It will include updates to improve overall performance and the ability to conduct transactions with local currency, as Microsoft Points will be retired later this year.
The sign up process is now accessed directly through your Xbox 360 console to streamline the experience. Space is limited, so once the spots are filled the beta will be closed to the public. To join, look for the Xbox Beta Program tile on the home hub of the Xbox Dashboard.
You will be required to agree to a non-disclosure agreement (NDA) for confidentiality reasons and there will be a helpful Beta FAQ that should show up here later today.