YouTube are beta testing a new "In This Video" annotations panel which will work on desktop and mobile.
The new annotation shows as a panel on the right of the video and has a close button in the same way as other annotations.
The exciting difference with this new format is that it is likely to work on mobile devices as well as desktop.
End cards are commonly used amongst YouTube Creators to encourage viewers to subscribe and watch more of their content. End cards are traditionally segments render in to the video and upload and they're made clickable using the spotlight annotation but, frustratingly, these annotations don't work on mobile devices.
It's hoped that theses new annotations will be an easy way for any creator to add related links in their videos without needing the technical know-how of adding picture in picture end cards in to their videos.