Sepolia Merge Announcement

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The Ethereum network is approaching one of its most transformative milestones: The Merge. As the second of three major public testnets to undergo this transition, Sepolia is now ready to shift from Proof-of-Work (PoW) to Proof-of-Stake (PoS). This pivotal event marks a critical step toward the full implementation of PoS on Ethereum’s mainnet, significantly improving scalability, security, and sustainability.

When the total difficulty (TD) of the Sepolia PoW chain exceeds 17,000,000,000,000,000, the network will officially transition to PoS — an event expected within days. Unlike previous upgrades, this merge requires coordination between both consensus layer (CL) and execution layer (EL) clients, making it essential for node operators, developers, and infrastructure providers to prepare accordingly.

Notably, post-merge, Sepolia will operate with a permissioned validator set, similar to existing Proof-of-Authority (PoA) testnets. In contrast, the upcoming Goerli/Prater merge will support an open validator set, allowing stakers to fully test the PoW-to-PoS transition in a public environment.

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Background: The Path to The Merge

Years of research and development have led Ethereum to its final testing phase before the mainnet Merge. With Ropsten already successfully merged and shadow forks running routinely, Sepolia's transition represents the next major checkpoint.

After Sepolia, only Goerli/Prater remains before the mainnet upgrade can proceed. Legacy testnets like Ropsten, Rinkeby, and Kiln will be deprecated following their merges, encouraging migration to active PoS-compatible environments.

The Merge differs from prior upgrades in two fundamental ways:

  1. Dual Client Updates: Node operators must update both their consensus and execution layer software.

  2. Two-Phase Activation:

    • Phase 1: Bellatrix upgrade activates on the beacon chain at a specific epoch.
    • Phase 2: Execution layer transitions at a predefined Terminal Total Difficulty (TTD) value.

Sepolia has already completed its Bellatrix upgrade, setting the stage for TTD activation.

Merge Timeline and Technical Details

Key Activation Stages

The transition unfolds in two stages:

1. Bellatrix Upgrade (Consensus Layer)

Initially, the TTD was set extremely high (1,000,000,000,000,000,000,000) due to Sepolia’s unstable hash rate — effectively preventing premature activation. After Bellatrix went live, the threshold was lowered to 17,000,000,000,000,000, a target expected to be reached within days.

2. Paris Upgrade (Execution Layer)

Once TTD is met or exceeded, the Paris execution-layer upgrade triggers. The next block will be produced entirely by beacon chain validators instead of miners.

⚠️ Due to fluctuating hash rates on testnets, exact timing may vary.

Following TTD achievement:

Applications can verify finalization using:

Infrastructure providers are advised to monitor both finalization status and overall network health during and after the transition.

Supported Client Versions

Node operators must run compatible versions of both consensus and execution layer clients.

Consensus Layer Clients

Execution Layer Clients

Client-Specific Configuration Notes

Besu

To support the updated TTD:

Erigon

For further details on TTD overrides, refer to prior guidance in the Ropsten TTD announcement.

Upgrade Specifications

Core changes are documented in:

Additional interoperability protocols:

Frequently Asked Questions (FAQ)

What should node operators do?

Post-Merge, every Ethereum full node must run both a consensus layer client (beacon node) and an execution layer client (e.g., Geth). These communicate via the Engine API over an authenticated JWT token.

If you previously ran only a beacon node or an EL client, you now need both components. Generate and configure the JWT token per your client’s documentation to enable secure communication.

Note: Running a beacon node ≠ running a validator client. Validators require both; regular nodes only need the beacon component.

Do stakers need to take action?

No immediate action is required for most stakers. Since Sepolia uses a permissioned validator set, only existing validators can participate.

However, for future open-testnet merges like Goerli/Prater:

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What should app and tool developers know?

Most dApps and smart contracts won’t break during The Merge. However:

Legacy testnets (Ropsten, Rinkeby, Kiln) will be deprecated — migrate to Goerli or Sepolia.

Should ETH holders worry?

No action is needed. This testnet upgrade does not affect Ethereum mainnet. Official announcements will be posted ahead of any mainnet changes.

What about miners?

Mining on Sepolia will cease once TTD is reached — expected in days. On mainnet, mining will end later this year during the final Merge.

Can I withdraw staked ETH after The Merge?

Not yet. Withdrawal functionality is planned for a subsequent upgrade (EIP-4895). The Merge focuses solely on consensus transition to minimize risk.

Where can I ask more questions?

Join the Merge Community Call on July 15 UTC for live Q&A with core developers and researchers.

Looking Ahead: Toward Mainnet

While no official date has been set for the mainnet Merge, progress on Sepolia and Goerli/Prater paves the way forward. Assuming smooth transitions:

  1. Goerli/Prater will merge with an open validator set.
  2. Once stable, Bellatrix will activate on mainnet with a defined TTD.
  3. Client teams will release production-ready versions.
  4. Final timelines will be announced across official channels — including this blog.

Any discovered issues or insufficient testing scope will delay progression until resolved.

This is more than an upgrade — it's a revolution in blockchain efficiency and decentralization.

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