Source: USGS Landsat Mission

Aug. 24, 2012 • A large metadata and file name update will be released on August 29, 2012. All access to Landsat data will be down for the day, with a return on August 30th. You can still view full resolution images through the LandsatLook Viewer.

Details:
https://landsat.usgs.gov/level-1-landsat-data-products-metadata