# Room 641A Room 641A was a secured room in an AT&T telecommunications facility in San Francisco publicly associated with allegations and evidence of infrastructure-level traffic copying for the National Security Agency. Former AT&T technician Mark Klein became the central public witness. ## Notebook evidence [[Scanned_20260730-1830]], PDF page 4, records Room 641A, AT&T, Mark Klein, PRISM, and STELLARWIND as adjacent nodes in an attempt to identify where collection occurs. ## Distinction Room 641A is evidence about a physical/network collection position. It should not be treated as the same program as PRISM or as a universal name for every AT&T–government surveillance relationship. ## Boundary Historical infrastructure evidence does not establish that any specific notebook subject's traffic traversed the facility or was retained, queried, or disseminated. ## Source - [[Scanned_20260730-1830]], PDF page 4.