Ethereum developers have confirmed that the Glamsterdam upgrade will go live on the Sepolia testnet on Oct. 6. At the same time, they warned that cheap test ETH could allow malicious builders to repeatedly win block auctions and then withhold the transaction payloads they promised to provide.
The Oct. 6 date was accepted during the Sept. 17 All Core Developers Consensus call after developers reviewed recent Glamsterdam testing.
The main concern involves EIP-7732, which introduces Enshrined Proposer-Builder Separation, or ePBS. The design separates the job of building transaction payloads from the validator’s consensus work and brings the relationship between builders and validators into Ethereum’s protocol rules.
Under ePBS, builders compete by submitting bids for the right to provide an execution payload. After a proposer accepts the winning bid, the builder is expected to provide the transactions behind that bid.
Consensus developer Potuz warned that the economics are very different on a public testnet because test ETH has little or no real market value. An attacker could create many builder identities, place very high bids, win the auctions and then refuse to provide the promised payload.
Because test ETH is cheap, the attacker could simply create new identities and repeat the process. Developers described this mainly as a testnet availability concern rather than a way to steal real ETH from Ethereum mainnet.
The discussion also raised questions about whether current client protections are strong enough. Some clients can switch to locally built blocks after several missed payloads, but developers were concerned that disposable builders could return under new identities and continue the behavior.
Developers did not describe this as a confirmed Sepolia exploit. Instead, they were discussing a possible problem that could appear once more outside participants begin testing ePBS on the public network.
Sepolia is useful for the first public Glamsterdam test because its validator set is relatively controlled. Hoodi is expected to follow and provides a more open validator environment for staking and protocol testing.
The latest schedule follows successful testing on Glamsterdam Devnet-11. The devnet completed its Gloas transition and increased the test gas limit from 60 million to 200 million without losing finality.
Devnet-11 used about 84,000 validators in a multi-client setup and included the main EIPs planned for Glamsterdam testing. The 200 million gas limit was a testing parameter and does not represent a confirmed mainnet limit.
Glamsterdam is designed to increase Ethereum Layer 1 capacity while changing how blocks are built and verified. EIP-7732 expands the execution-payload propagation window from roughly two seconds to around nine seconds, giving nodes more time to distribute and verify larger payloads.
The upgrade also includes Block-Level Access Lists and several gas-pricing changes. These changes could require updates from wallets, indexers, gas estimators and smart contracts that depend on older gas assumptions.
The Sepolia schedule also gives client teams a shorter review period than usual. Developers discussed Sept. 29 as the latest target for Sepolia-ready client releases, leaving only seven days before the Oct. 6 activation.
Ethereum developer Fredrik Svantes noted that the normal process recommends at least 14 days between release-ready client software and a public testnet fork. That time is normally used for security reviews, bug-bounty testing and outside security work.
Developers accepted the shorter window for Sepolia partly because its validator set is more controlled and the network can be recovered more easily if problems occur. Core developer Alex Stokes encouraged teams to release their software as early as possible so reviewers have more time to test it.
The shorter schedule comes after several testing problems during earlier Glamsterdam devnets. Some tests experienced non-finality or client issues, leading developers to make fixes and run additional testing before reaching Devnet-11.
Glamsterdam is still targeted for the fourth quarter of 2026, but Ethereum has not set a mainnet activation date, epoch or final timestamp.
After Sepolia, developers expect to move to Hoodi, with its timing depending on how the Sepolia activation performs. Any major problems during the public test could affect the following schedule.
For now, the next major milestones are the Sept. 29 client software target and the Oct. 6 Glamsterdam activation on Sepolia. The mainnet date remains unconfirmed.
