iOS 8.4 to launch 8am PT on Tuesday 30th June. Beats 1 to follow at 9am PT.
Update: A new build of iOS 9 will also be seeded on June 30th:
@lokithorrrrr a new iOS 9 seed will support Apple Music— Eddy Cue (@cue) June 27, 2015
“Tuesday morning we’ll be unveiling the next chapter. Please make a note to upgrade to iOS 8.4 at 8am PT Tuesday, June 30th and listen to the first Beats 1 broadcast at 9am PT.”