This article explains it all!

https://medium.com/@eossov/sov-becomes-first-immutable-currency-token-on-eos-mainnet-5827a2937ebf

In addition to being the only variable-rate self-deflationary cryptocurrency, SOV is now the first currency token on EOS to turn permission of the contract over to EOSIO*. Transaction ID 769034492d3fd1267a3064954f2ee400cbe5b9751dc559f5d1072c4f3a377796. This makes changes impossible without 15/21 BP approval and fully decentralizes SOV.

SOV had a starting supply of 1 billion and at the time of writing this, it is at 984,862,536.8652 SOV just a bit more than 2 weeks later.

Nasdaq Article on EOS the token whose Block Producers (Miners/Block Signatures) SOV has its permissions signed over to

https://www.nasdaq.com/articles/five-big-questions-eos-answered-2018-11-14