When is a mirror not a mirror? When it is the rear-view mirror in the new Cadillac CT6.

The American luxury automaker's new flagship sedan has a mirror that can toggle between being a traditional mirror and a monitor for a rear-facing camera that delivers a wider view of the road behind than the old-fashioned mirror can.

The National Highway Traffic Safety Administration just gave its okay to the technology, the first instance of an automaker proposing to replace--even part-time--the inside rear-view mirror.  

The CT6 is the first Cadillac model directly aimed at German luxury cars like the Mercedes-Benz S Class, BMW 7-series and Audi A8. It goes on sale next month, with loaded models expected to cost nearly $90,000.