Introduced by twitter IIRC. When used it generally means you've hit some sort of rate limit. 429 "Too Many Requests" is usually more appropriate. The code had

Introduced by twitter IIRC. When used it generally means you've hit some sort of rate limit. 429 "Too Many Requests" is usually more appropriate. The code had a previous (now deprecated and possibly no more official when it was in use) hence the gap in the list of official codes.