It’s not official by any means. In fact, the only real announcement for it comes from the Twitter feed of REM bassist, Mike Mills. That said, word has come down that David Letterman will soon be announcing his retirement in 2015.
Letterman is the current title holder for the longest working late night host, having spent 32 years on the air between NBC and CBS. Let the replacement speculation begin. I hear Jay Leno has some free time.