Kusama network started as a Proof-of-Authority network and was transitioned to Proof-of-Stake on 28 October 2019 at approximately 18:43 Zurich time (CET). The first successful validator set rotation took place at 22:45 CET.
Currently, Kusama is a healthy Proof-of-Stake network with over 150 validators and over a million blocks produced.
The rollout of full functionality of Kusama was staggered to allow for a safe transition. The first PoS phase began with 20 validators. Of the 20, the Web3 Foundation ran nine and Parity Technologies ran six. Five were ran by highly staked community members as voted in by the Phragmen election.
When the initial transition was successful, additional validator spots were opened 10 at a time in order to allow for more validators to enter the active set.
When the first transition to PoS took place, the full functionality of Kusama was not fully available. Notably, the Sudo key still existed and was used to initiate further upgrades. Balance transfers were still disabled for a short while.
Kusama now has had its full functionality enabled.