Ethereum developers have confirmed that the Glamsterdam upgrade will first be activated on the Sepolia testnet on October 6, followed by deployment to Holesky. However, prior to public testing, the team has warned that low-cost test ETH may amplify builder abuse, potentially impacting block production stability on the testnet.
Risk is concentrated in EIP-7732.
The core of this discussion is EIP-7732, the protocol-integrated proposer-builder separation (ePBS) mechanism introduced by Glamsterdam. This design separates the responsibilities of block transaction packaging and validator consensus, with builders submitting bids first, followed by proposers selecting the winning bid.
By design, the winning builder is required to continue broadcasting the corresponding transaction payload. If a builder wins but refuses to deliver, the network will not directly lose mainnet funds, but testnet availability may be disrupted.
At the core developers meeting on September 17, developer Potuz stated that the testnet environment differs from the mainnet. Attackers can obtain test ETH at almost no real cost, allowing them to create numerous builder identities, submit bids far above normal participants' prices, repeatedly win bids, and then intentionally fail to deliver payloads.
Existing safeguards or shortcomings
Developers believe this is more likely a stability issue that may surface during the public test phase, rather than a confirmed Sepolia vulnerability. While some existing clients have implemented circuit breakers, certain solutions only revert to local block building after missing multiple consecutive payloads.
Potuz also mentioned that he is unaware of any unified protection measures currently available for all clients that can directly block individual malicious builders. For application teams and infrastructure teams relying on testnet validation software, this means Sepolia may require stronger protections under ePBS conditions.
Sepolia currently employs a permissioned set of validators, primarily controlled by clients and testing teams; Hoodi, on the other hand, offers an open validator environment, making it more suitable for staking and protocol upgrade testing. This also means that if Sepolia encounters issues during its first long-term public deployment, developers still have greater flexibility to address them.
Devnet-11 has completed a 200 million Gas exercise.
Before entering Sepolia, Glamsterdam's Devnet-11 underwent a controlled environment test. After the Gloas transition, the testnet increased the block gas limit from 60 million to 200 million and operated with approximately 84,000 validators in a multi-client configuration.
According to reports, the transition was completed without losing finality. However, the 200 million Gas limit is currently only a test parameter and does not indicate that the Ethereum mainnet has officially adopted this cap.
One of Glamsterdam’s goals is to enhance Ethereum Layer 1 throughput while modifying block building and validation processes. According to the current specifications, EIP-7732 will extend the execution payload propagation window from approximately 2 seconds to about 9 seconds, giving nodes more time to distribute and verify larger payloads.
In addition to ePBS, this upgrade includes block-level access lists and several Gas pricing adjustments. Previous compatibility testing has shown that some wallets, indexers, Gas estimation tools, and contracts relying on fixed Gas assumptions may need to be adapted and retested before the upgrade.
Only 7 days remain until client preparation is due.
Developer Fredrik Svantes stated at the conference that the standard process typically requires clients to reach release-ready status at least 14 days before the first public testnet activation, to allow time for internal security reviews, bug bounty exposure, and external security audits. However, the preparation window for Sepolia has been shortened to 7 days.
Under the current schedule, the client team must release a Sepolia-compatible software version by September 29, followed by a fork test on October 6. Core developer Alex Stokes has urged the team to deliver as early as possible to allow more time for review.
The timeline was compressed and also related to issues encountered in previous rounds of testing. Earlier tests, including Devnet-8, Devnet-9, and Platåberget, experienced cases of non-finality and node downtime, prompting the team to continue addressing edge cases prior to Devnet-11.
The mainnet launch time has not yet been determined.
Ethereum’s public roadmap still lists Glamsterdam for Q4 2026, but the mainnet activation date has not been confirmed. The only next confirmed upgrade at this time is the Sepolia upgrade on October 6.
Hoodi will proceed after Sepolia, but the exact timing still depends on the results of the previous phase. Developers have not yet announced the mainnet fork epoch or final activation timestamp; successfully completing the multi-client tests remains a prerequisite for setting the mainnet date.