You're both right, its a collaboration between the two:
>For the MUSCULAR project, the GCHQ directs all intake into a “buffer” that can hold three to five days of traffic before recycling storage space. From the buffer, custom-built NSA tools unpack and decode the special data formats that the two companies use inside their clouds. Then the data are sent through a series of filters to “select” information the NSA wants and “defeat” what it does not.
