Ann Oldenburg

USA TODAY

Get ready to say goodbye to Diane Sawyer at ABC's World News desk.

And hello to David Muir.

ABC News today announced new roles for Sawyer, 68; Muir, 40; and George Stephanopoulos, 53.

Sawyer will be "stepping aside" to lead "new programming tackling big issues and extraordinary interviews," says the announcement from ABC President James Goldston.

Muir will become anchor and managing editor of World News, starting Sept. 2.

Stephanopoulos, anchor of Good Morning America and This Week, has been promoted to chief anchor of ABC News, handling special reports and breaking news. (Don't worry, GMA fans, he'll still be doing the morning gig.)

"After wonderful years at World News I decided it is time to move to a new full time role at ABC News," says Sawyer in the announcement.

She says she'll be "dedicated to enterprise reporting, innovative approaches to breaking news and new ways of thinking about big issues and events around the world."