WebAssembly First Public Working Drafts | W3C News https://www.w3.org/blog/news/archives/6838
The 451 status code is now supported | GitHub Developer Guide https://developer.github.com/changes/2016-03-17-the-451-status-code-is-now-supported/
GitHub now returns a 451 HTTP status code for repos that have been blocked/removed due to a DMCA notice.
The new 451 code should be used in place of a generic 403 to indicate that content is not available for legal reasons. The reason is likely to be a DMCA notice, but could be used for content that has license restrictions, or other legislative or regulatory blocks.