Ethereum Glamsterdam Upgrade: Sepolia Activation, Key Changes and Mainnet Timeline
2026-10-05
The Ethereum Glamsterdam upgrade is set to activate on the Sepolia testnet on 6 October 2026 at 13:53:36 UTC.
This marks the first public testnet deployment of one of Ethereum's most ambitious protocol changes in recent history, combining execution layer and consensus layer improvements under a single hard fork.
The upgrade targets a 200 million gas limit floor, more than three times the current ceiling. Here is what Glamsterdam changes, where development stands, and when mainnet could follow.
Key Takeaways
- Glamsterdam activates on Sepolia testnet on 6 October 2026 at 13:53:36 UTC, at epoch 353,024 and slot 11,296,768.
- The upgrade introduces ePBS (EIP 7732) and Block Level Access Lists (EIP 7928) to improve scaling and block production.
- Mainnet activation is targeted for Q4 2026, with the Hoodi testnet tentatively scheduled for 27 October, pending Sepolia results.
What Is the Ethereum Glamsterdam Upgrade?
The Glamsterdam upgrade is Ethereum's next major hard fork following the Fusaka upgrade. It merges the Amsterdam execution layer changes with the Gloas consensus layer changes into a single coordinated protocol update. The name "Glamsterdam" reflects this combination.
The primary objective is to expand Layer 1 capacity without compromising Ethereum's security or decentralisation.
Rather than relying solely on Layer 2 networks to handle growing demand, Glamsterdam strengthens the base layer by redesigning how blocks are created, validated, and propagated across the network.
The upgrade includes ten EIPs covering block production, gas pricing, state management, and networking between Ethereum nodes.
The most significant proposals are EIP 7732 (Enshrined Proposer Builder Separation) and EIP 7928 (Block Level Access Lists), both designed to lay the groundwork for Ethereum to safely process significantly larger execution payloads.
One of the biggest goals is preparing Ethereum for a gas limit target of 200 million, up from the current ceiling of 60 million. This would represent more than a threefold increase in per block capacity.
Achieving this safely requires restructuring core processes so that higher throughput does not create unsustainable demands on node operators.
The upgrade also addresses sustainability. As Ethereum continues growing, the protocol must prevent excessive database expansion while allowing more transactions through each block.
Glamsterdam restructures gas accounting and state pricing through EIP 8037, ensuring that the cost of creating new state more accurately reflects its impact on the network.
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How Do ePBS and Block Level Access Lists Improve Ethereum?
The headline feature of Glamsterdam is Enshrined Proposer Builder Separation (EIP 7732), often shortened to ePBS.
Currently, the relationship between block builders and validators relies heavily on external relay infrastructure.
ePBS moves this relationship directly into the Ethereum protocol, incorporating commitments, reveals, timeliness attestations, and proposer payments into protocol mechanics rather than depending on external exchanges.
This change reduces trust assumptions while giving validators more time to verify blocks. The longer propagation window, extending from approximately 2 seconds to around 9 seconds, makes it possible for Ethereum to safely handle much larger execution payloads.
ePBS does not eliminate all external builder services or relay functions, but it brings the most critical parts of the block production pipeline under protocol level rules.
The second major proposal is Block Level Access Lists (EIP 7928). These provide validators with an upfront map showing which accounts and storage locations every transaction in a block will access before execution begins.
As transaction dependencies become known in advance, clients can prepare data more efficiently and eventually validate many independent transactions in parallel rather than processing everything sequentially.
Parallel processing is widely viewed as one of Ethereum's most important scaling technologies. While Glamsterdam does not fully introduce parallel execution, it establishes the infrastructure that future upgrades will build upon.
During Devnet 11 testing, the Nethermind execution client completed all 2,302 performance tests for Block Level Access Lists, processing 570.7 billion gas in 3 minutes and 15 seconds.
These results demonstrate that the access list mechanism can handle the throughput demands of a 200 million gas environment.
What Happened During Glamsterdam Devnet Testing?
The path to Sepolia has been longer and more complex than developers originally planned.
Glamsterdam's original mainnet target was June 2026, and the first Sepolia activation was scheduled for 3 August 2026. Both dates slipped as technical challenges emerged during private development networks.
Ethereum ran nine sequential devnets (Devnet 0 through Devnet 9) between March and September 2026.
None of these achieved stable finality under the full Glamsterdam rule set. Devnet 8 experienced finality issues during its Gloas activation, and Devnet 9 encountered unplanned non finality before teams could resolve the underlying problems.
Developers skipped Devnet 10 entirely, determining that the scope of required fixes warranted a fresh configuration rather than an incremental patch.
Devnet 11 launched on 14 September 2026 with 84,000 validators, an increase 84 times greater than Devnet 9, representing the closest approximation to mainnet conditions tested to date.
Devnet 11 completed its Gloas transition on 16 September and subsequently raised the gas limit from 60 million to 200 million without losing finality. This successful rehearsal cleared the critical milestone needed before proceeding to Sepolia.
However, Devnet 11 was designed as a controlled rehearsal rather than an adversarial stress test. The 200 million gas limit has not been tested under deliberate attack conditions.
Developers have also flagged that production grade builder infrastructure from major relay teams has yet to successfully complete Glamsterdam fork transitions, adding another variable to the timeline.
What Is the Glamsterdam Mainnet Timeline?
The Sepolia activation on 6 October is the first of at least two public testnet deployments before mainnet. The Ethereum Foundation confirmed the Sepolia date on 28 September 2026, setting activation at epoch 353,024.
Here is the current milestone schedule:
- Sepolia testnet activation: 6 October 2026 at 13:53:36 UTC (confirmed).
- Hoodi testnet activation: tentatively 27 October 2026 (contingent on stable Sepolia results).
- Mainnet activation: Q4 2026 target, with December 2026 discussed as the earliest possibility (unconfirmed).
Node operators running Sepolia validators must upgrade both execution and consensus layer clients before activation.
Confirmed compatible client versions include Lodestar 1.49.0, Prysm 7.2.0, and Teku 26.9.1 on the consensus layer, alongside Besu 26.9.0, Erigon 3.7.0, go ethereum 1.17.6, Nethermind 2.0.0, and Reth 2.7.0 on the execution layer.
The mainnet date remains conditional on several factors. Stable operation following the Sepolia activation is the first requirement. A successful Hoodi testnet deployment must follow.
Developers have consistently stated that correctness takes priority over the calendar, and previous slippages demonstrate their willingness to delay rather than ship known instability.
Developers have also warned that Sepolia's freely available testnet ETH and easily replaceable builder identities could allow attackers to repeatedly disrupt Glamsterdam's block building auctions by withholding promised transaction payloads.
This testing risk does not threaten mainnet funds but could complicate or stall the evaluation of ePBS mechanics during the testnet phase.
Why Does the Glamsterdam Upgrade Matter for ETH Users?
Most ETH holders will not need to take any action during the upgrade. Wallet balances, smart contracts, and tokens will continue operating normally after compatible clients update their software.
Validators benefit from several protocol improvements. Proposed changes shorten validator exit queues, improve block production reliability, and reduce disruption during rare slashing events.
The shift to protocol level proposer builder separation also gives validators a more predictable and transparent role in block construction.
Developers gain a more efficient foundation for building decentralised applications. Better gas accounting, improved state management, and enhanced networking support larger applications without creating unnecessary pressure on node operators.
The groundwork for parallel transaction validation could eventually unlock significant performance gains across the ecosystem.
Users could experience lower transaction costs as the increased gas limit allows more transactions per block, reducing competition for block space during periods of high activity.
Additional improvements also make wallet infrastructure, cross chain deployments, and onchain tracking easier for developers and service providers.
The Sepolia activation represents an important checkpoint rather than the final launch. Public testing allows client teams, infrastructure providers, and application developers to identify issues before the hard fork reaches Ethereum mainnet.
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Conclusion
The Ethereum Glamsterdam upgrade represents one of the most ambitious protocol changes in the network's history. The Sepolia testnet activation on 6 October 2026 brings ePBS, Block Level Access Lists, and a 200 million gas limit target into public testing for the first time.
With the Hoodi testnet tentatively following later in October and mainnet targeted for Q4 2026, Ethereum is on track for a significant capacity expansion before the end of the year.
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FAQ
When Is the Glamsterdam Sepolia Activation?
The Glamsterdam upgrade activates on the Sepolia testnet on 6 October 2026 at 13:53:36 UTC, at epoch 353,024.
What Is the Glamsterdam Mainnet Date?
No confirmed mainnet date has been set, but Ethereum's public roadmap targets Q4 2026, with December 2026 discussed as the earliest possibility.
What Is EIP 7732?
EIP 7732 introduces Enshrined Proposer Builder Separation, bringing block building commitments and validator payments directly into the Ethereum protocol.
What Are Block Level Access Lists?
Block Level Access Lists (EIP 7928) provide validators with upfront transaction dependency information, enabling more efficient data preparation and laying the groundwork for parallel execution.
Do ETH Holders Need to Do Anything?
Most ETH holders do not need to take any action, as wallet balances and tokens will continue operating normally after node operators upgrade their client software.
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