The hybrid casper (FFG) implementation is moving towards full casper (CBC) says Vitalik Buterin, ethereum’s inventor.
“Since two weeks ago it already uses a variant of GHOST as the fork choice rule,” he added in a public comment.
Ghost is a protocol that modifies the “longest chain” rule with a “heaviest subtree” rule which accounts for all blocks, including orphaned blocks (uncles), in measuring total difficulty, so increasing security.
The speed of development thus might suggest that Casper FFG is perhaps no different than Casper CBC by the time it launches due to a considerable re-design that merges Casper and Sharding into shasper.
From our understanding of the specification , at a high level view there will be a Proof of Stake (PoS) beacon chain that manages validation and the shards, with the Proof of Work (PoW) chain connecting to it through a smart contract for the staking deposit. Buterin however says:
“The PoW chain already plays no part in the new design. The goal is that eventually it would turn into some kind of sidechain or contract on the PoS chain.”
Much, therefore, appears to be in flux with the specification not yet finalized as far as we are aware, but a lot of work appears to be ongoing.
A developers meeting on sharding this Thursday has no fewer than seven different teams implementing sharding.
One of them says they have a full beacon node running, but most appear to be working on the implementation of the beacon chain.
It appears plenty of work is left to be done, with research on-going, including on fork-choice rules and randomness beacon.