The 451 status code is now supported | GitHub Developer Guide
developer.github.com/changes/2016-03-17-the-451-status-code-is-now-supported
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
GitHub API will now respond with a 451 status code for resources it has been asked to take down due to a DMCA notice.