When they have had an alumni program, they specify the details around the same time as when they let everyone know they can apply for fall/fall advantage.
they always say that they don't know if one will exist or not (because they probably don't).
then when they release the details stuff varies. these are things like the roles that are available (never the full list. sometimes one or two. sometimes 5). the date or dates that one must be available (recently was only one arrival date, but they have had 2 as well). then any other requirements (do you have to be enrolled in school?) and how to apply (special proceedure or follow the steps as other applicants).
they basically got rid of the summer only program about 12 years ago. they haven't always had something for alumni since then.
this was the first year in several years that they haven't, though. I'd guess that it is very unlikely that they will be able to offer one this year.