Sawyer, 63, is slated to start her new job as "World News Tonight" anchor Dec. 21. Current anchor Charles Gibson is retiring and his last day will be Dec. 18.
TVGuide.com said Sawyer estimated she has appeared on 2,881 editions of "GMA" in 10 years.
"You're really giving up your day job, after all this time," the television industry magazine quoted "GMA" co-anchor Robin Roberts as saying to Sawyer on Monday's program. "It is so difficult. ... Thank you. We're going to do all things just like you this week. We're going to have fun. We're going to look back."
Sawyer's "GMA" replacement has not yet been named.