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As they stated that the new SSDs are PCI-e based and only Apple has the device, there's no way to upgrade yourself. 3rd party suppliers such as OWC might provide one in the future, but at the moment you're out of luck.

However, no one has opened one of the new rMBPs yet so ... but assuming the rMBP uses the same type of SSD connection as the current MBA..
 
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