In the words of Danny Ryan, Altair is here and the Merge is coming!
We first simulated the merge back in April/May of this year.
Fast forwards 5 months and we're finally ready for a more realistic follow-up.
This time, the interop will build off Altair, rather than Phase 0.
Importantly, we'll be testing the transition mechanism that will take us from a pre to post merge world.
We also have a 5th client on the block :)
Merge quick sync
In general an Ethereum client consists of two layers - the consensus layer and the execution layer.
The consensus layer is responsible for the consensus, i.e. block validity, and fork choice rule. As it stands, on mainnet, we rely on PoW consensus. The Merge enables PoS consensus driven by the beacon chain.
The execution-layer is responsible for transaction bundling, execution, and state management. During the merge this layer will be represented by modified pre-merge PoW clients (eg. geth, nethermind, besu, openethereum, turbogeth, etc).
The key to a successful merge is getting these two layers to talk to each other: the plan right now is for them to interact via a one-way communication protocol, driven by the consensus layer (although this approach is not yet set in stone).
Note that if these layers are bundled into a single piece of software, then the UX of running a post-merge client becomes very similar to running a pre-merge PoW client today (which is precisely why we are working so hard on building out our execution layer client).
If you'd like to to dig into the details, this document specifies the modifications that must be made to beacon chain and pre-merge clients to turn them into a post-merge consensus node and execution engine, respectively.
And while we're waiting for a compatible execution client, we have everything you need to start experimenting on the consensus side.
You can keep track of our broader progress here.
Interop lock in: round 2
In the words of Ben Edgington, the cat is out of the bag - the eth1 and eth2 client teams will be meeting up in early October to get some Merge devnets running.
You can think of this as round 2 of the interop event we did two years ago.
Expect to hear a lot of updates from the client teams as we build out the Merge logic and test our software together on short-lived devnets.
In anticipation, we'll leave you with some highlights from the previous lockin.
P.S. Keep your eyes peeled for an Ethereum Foundation blogpost on Monday. This will include all mainnet Altair releases. We will also be making a more formal Altair announcement next week.