The PoS protocol itself has been running in production since December 1, in parallel with the old network, with over $10 billion staked so far. What remains is

The PoS protocol itself has been running in production since December 1, in parallel with the old network, with over $10 billion staked so far. What remains is to change the legacy clients to use the PoS network for choosing blocks, instead of miners. That has a working multi-client testnet.