Not sure at this point when or if Grantcoin will implement Proof of Stake. It depends mostly on the economic model of the coin and how a switch to PoS would affect its charitable purpose, i.e. whether it would tend to increase or decrease the amount of GRT being distributed as rewards for maintaining the network, vs. how much is being distributed as Basic Income grants. The Grantcoin Foundation Board of Directors has had some discussions about this in the past couple of months, but a final decision has not yet been made.

For the foreseeable future, Grantcoin will remain PoW only.