HomeEtherumAnnouncement: Merge of Sepolia on Ethereum Foundation Blog

Announcement: Merge of Sepolia on Ethereum Foundation Blog

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Note: on July 5, 2022, the recommended releases for go-ethereum and Erigon were modified. See “Client Releases” for details.

Sepolia will be the second of three public testnets to run through The Merge.

The network will transition to proof-of-stake when the total difficulty on the proof-of-work chain exceeds 17,000,000,000,000,000, which is expected to occur around in the next few days.

Post-merge, Sepolia will have a permissioned validator set, like existing proof-of-authority testnets. Goerli/Prater, which will merge at a later date, will maintain an open validator set to allow for stakers to test the transition.

Background

After years of work to bring proof-of-stake to Ethereum, we are now well into the final testing stage: testnet deployments! With Ropsten already transitioned to proof-of-stake and shadow forks continuing regularly, Sepolia is now ready for The Merge. After Sepolia, only Goerli/Prater will need to be merged before moving to mainnet. Other testnets will be considered deprecated post-merge, as explained in a recent post.

The Merge is different from previous Ethereum upgrades in two ways. First, node operators need to update both their consensus layer (CL) and execution layer (EL) clients in tandem, rather than just one of the two. Second, the upgrade activates in two phases: the first at an epoch height on the Beacon Chain and the second upon hitting a Total Difficulty value on the execution layer.

Sepolia has already run through the Bellatrix upgrade on the Beacon Chain. We now announce the details of the second phase of the transition: hitting the Terminal Total Difficulty.

Upgrade Information

Timing

The Merge is a two-step process. It starts with a network upgrade on the consensus layer, triggered by an epoch height. This is followed by the execution layer’s transition from proof-of-work to proof-of-stake, triggered by a specific Total Difficulty threshold, called the Terminal Total Difficulty (TTD).

On June 20, 2022, at epoch 100, the Bellatrix upgrade prepared the Sepolia Beacon Chain for The Merge. At that point, CL clients began listening for a TTD value to be hit on the proof-of-work chain. Because the hash rate of proof-of-work testnets is very volatile, the TTD value was first set to an exceedingly high value, 100000000000000000000000. At Sepolia’s current hash rate, it would take hundreds of years to reach this value. With Bellatrix now live, an updated TTD value of 17000000000000000 has been chosen for the transition. It is expected to be hit within the next few days. When this new TTD is hit or exceeded, the execution layer part of the transition, codenamed Paris, will start. Again, note that hash rate on Sepolia is notoriously variable, so the actual time at which the Terminal Total Difficulty takes place may fluctuate.

Once the execution layer has exceeded the TTD, the next block will be solely produced by a Beacon Chain validator. We consider The Merge to have been completed once the Beacon Chain has finalized this block. Assuming normal network conditions, this should happen 2 epochs, or approximately 13 minutes, after the first post-TTD block is hit! A new JSON-RPC block tag, finalized, returns the latest finalized block or an error if no such post-merge block exists. This tag can be used for applications to check if The Merge has been completed. Similarly, smart contracts can query the DIFFICULTY opcode (0x44), renamed to PREVRANDAO post-merge, to determine if The Merge has happened. We recommend infrastructure providers monitor overall network stability in addition to finalization status.

Client Releases

The following client releases support The Merge on the Sepolia testnet. Node operators must run both an execution and consensus layer client to remain on the network during and after The Merge. When choosing which client to run, validators should be especially mindful of the risks of running a majority client on both the EL and CL. An explainer of these risks and their consequences can be found here. An estimate of current EL and CL client distribution and guides for switching from one client to another can be found here.

Consensus Layer

Execution Layer

Name

Version

Link

Besu

See “Besu Note” below

See “Besu Note” below

Erigon

v2022.07.01

Download

go-ethereum (geth)

v1.10.20 master

See “Geth Note” below

Nethermind

1.13.4

Download

Besu Note: to be compatible with the Sepolia merge, Besu users will need to perform a manual Terminal Total Difficulty override. To do so, users should run the latest Besu release, 22.4.3 as of the publication of this post, and do the following:
If using TOML configuration files, add the following line: override-genesis-config=[“terminalTotalDifficulty=17000000000000000”]
If starting the node using the CLI, add the following flag: –override-genesis-config=”terminalTotalDifficulty=17000000000000000″
More information about overriding the TTD can be found in the Ropsten TTD Announcement.

Geth Note: a regression introduced in go-ethereum v1.10.20 makes it unsuitable for use as part of the Sepolia merge. Users of Geth should instead run the master branch until a new release is out. Instructions to do so are available here.

Upgrade Specifications

Consensus-critical changes for The Merge are specified in two places:
The consensus layer changes, under the bellatrix directory of the consensus-specs repository
The execution layer changes, under the Paris spec in the execution-specs repository

In addition to these, two other specifications cover how the consensus and execution layer clients interact:
The Engine API, specified in the execution-apis repository, is used for communication between the consensus and execution layers
Optimistic Sync, specified in the sync folder of the consensus-specs repository, is used by the consensus layer to import blocks as the execution layer client is syncing and to provide a partial view of the head of the chain from the former to the latter

FAQ

As a node operator, what should I do?

Post-merge, an Ethereum full node will combine a consensus layer client, which runs the proof-of-stake Beacon Chain, and an execution layer client, which manages the user-state and runs the computations associated with transactions. These communicate over an authenticated port using a new set of JSON RPC methods called the Engine API. The EL and CL client authenticate each other using a JWT secret. Node operators should refer to their clients’ documentation for instructions about how to generate and configure these.

In other words, if you were already running a node on the Beacon Chain, you now also need to run an execution layer client. Similarly, if you were running a node on the current proof-of-work network, you will need to run a consensus layer client. For them to communicate securely, a JWT token must be passed to each client.

It is worth emphasizing that while they are both part of consensus layer client releases, running a Beacon Node is distinct from running a Validator Client. Stakers must run both, but node operators only need the former. This post explains the difference between both components in more detail. Also, note that each layer will maintain an independent set of peers and expose its own APIs. The Beacon and JSON RPC APIs will both continue working as expected.

As a staker, what do I need to do?

Sepolia’s validator set is permissioned, so unless you have already been included as a Sepolia validator, no action is required. Goerli/Prater’s transition to proof-of-stake, which will be announced at a later date, will be open to all validators. Below are some notes to prepare for this. Again, no action is required now.

As explained above, validators on the Beacon Chain will need to run an execution layer client after The Merge, in addition to their consensus layer clients. Pre-merge, this was strongly recommended, but validators could have outsourced these functions to third-party providers. This was possible because the only data required on the execution layer were updates to the deposit contract. Post-merge, validators need to ensure that transactions in blocks that they create and attest to are valid. To do this, each beacon node must be paired with an execution layer client. Note that multiple validators can still be paired to a single beacon node & execution layer client combo.

While this expands validators’ responsibilities, it also gives a validator who proposes a block the right to its associated transaction priority fees (which currently go to miners). While validator rewards accrue on the Beacon Chain and will require a subsequent network upgrade to be withdrawn, transaction fees will continue to be paid, burned, and distributed on the execution layer. Validators can specify any Ethereum address as a recipient for transaction fees. After updating your consensus client, be sure to set the fee recipient as part of your validator client configurations to…

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