The California Public Utilities Commission approved on October 20, 2011 the introduction of an overlay area code as a relief plan for existing NPA 408 serving cities such as Santa Clara, Cupertino, San Jose, Sunnyvale. The new area code 669 will cover the exact same area currently covered by area code 408. As a result 1+10 digit dialing will be the dialing format for residents of this area. Permissive 1+10 digit dialing in area code 408 will commence on April 21, 2012 and end on October 20, 2012 when 1+10 digit dialing becomes mandatory. The new area code 669 will officially be activated on November 20, 2012.
See official NANPA announcement and map of the new overlay complex (PDF document)