Sitestreams was updated last night to require HTTP 1.1. The notifications for this were sent in May, months ago. Sometime that posting was quietly updated to say that it would happen Nov 6th. It was done Nov 21st.
It’s been a painful morning for me.
As far as I can tell, there was no warning from @twitterapi or via the email / posting channels that you sometimes use, in Nov, of the new deploy date. Having some more timely advanced warning (a few days ahead of the deploy) of such changes would be really helpful - in order to prepare for watching the transition.