The next release (Metropolis) will afaik contain a first implementation of proof of stake which will run in parallel with their proof of work algorithm (last I heard was that every 1000th transaction will be run via proof of stake, but I may be wrong here).
https://github.com/ethereum/casper
There's even a Github project where you can see that the current state is work on the "Fork choice/chain logic". This was started 6 days ago:
https://github.com/ethereum/casper/projects/1
The next release (Metropolis) will afaik contain a first implementation of proof of stake which will run in parallel with their proof of work algorithm (last I heard was that every 1000th transaction will be run via proof of stake, but I may be wrong here).