http://www.theverge.com/2017/3/16/14953756/youtube-annotations-feature-discontinue-cards-end-screens
So, Youtube is removing the annotations features on May 2nd. reasons varies. They say it's outdated and it doesn't work on mobile. Instead, they may use the cards feature and the end screens. While they are removing the ability to add or edit annotations, existing one will remain.
While I get some people hate annotations due to popping up on videos (though you can just turn it off in the video settings…), I'm kinda sad they are gone. Mostly because it will result in the death of one of my most favorite channel, the Annotated series. Those guys really use those annotations to max comedy potential and creative use of it. It's sad to see their main tool gone and no annotations on this channel feels like losing on what made it special and awesome.
Thankfully, the channel may have a back up plan and are releasing the final few episodes of Kirby as well as letting fans choose the videos for the final intermission month.
Here's the video: