Currently, public sub counts are abbreviated in most but not all places across YouTube. In August, we’ll make this more consistent by always showing abbreviated sub counts publicly. Creators: You’ll still see your full sub count in Studio! Learn more → http://yt.be/help/abbrev-count …pic.twitter.com/pmaKk4EU4k
Literally no one wants this. Please don't do this and listen to the community for once. Perhaps this can be an optional setting for people who like rounded numbers, but don't force it on everyone and don't mess up the API.