https://www.apple.com/apples-commitment-to-customer-privacy/
In addition the new section launched today includes a page on government information requests, including "National Security Orders from the U.S. government." One sentence summary: they provide data to the government when required to by law.
PRISM itself is a program that is structured as a request/response, and the requests are approved by the FISA court, so it would fit into Apple's language in that section.
The initial report of PRISM implied that the NSA and FBI had direct, unfettered access to providers' "central servers", but that has been since walked back a bit. The points of concern with PRISM are 1) poor oversight from the FISA court, 2) overly broad request criteria resulting in huge datasets collected, and 3) the lack of public oversight due to gag orders.