Clear Channel's "big announcement" for iHeartRadio has been revealed: The company will host a multi-act, multi-format, two-day concert—dubbed the iHeartRadio Music Festival—Sept. 23-24 at the MGM Grand in Las Vegas. The company is billing the festival as "the biggest live music event in radio history."

The event is being staged to launch an updated version of iHeartRadio, which will be available this fall. It will include not just existing radio station streams, but "custom radio, like Pandora but with more songs, more control and no commercials through the end of the year."
The concert, which will be streamed live on iHeartRadio.com and via the app for smartphones and iPads, will be headlined by Lady Gaga, Coldplay, Jennifer Lopez, Steven Tyler, Kenny Chesney, Carrie Underwood, The Black Eyed Peas, Alicia Keys and Rascal Flatts. Also on the bill: Usher, John Mayer, Jane's Addiction, Kelly Clarkson, Sting, Bruno Mars, Nicki Minaj, David Guetta, and Sublime with Rome. More performers will be announced through the summer. Tickets go on sale Saturday, July 16 via Ticketmaster. But Clear Channel is suggesting fans "like" iheartRadio on Facebook now, to stay in touch with the event and learn about how to win a concert package.