Ethereum Sets October 6 for Glamsterdam Test as Fake Builders Threaten Network Testing
Ethereum developers have scheduled October 6 for the Sepolia test of the upcoming Glamsterdam upgrade, but a potential attack involving fake block-builder identities could disrupt the network’s dress rehearsal.
During Thursday’s core developer call, Ethereum consensus developer Potuz warned that an attacker could use free test ether to create thousands of fake builders, submit aggressive bids and repeatedly win the right to produce blocks. The attacker could then withhold the transaction data needed to complete those blocks, leaving the network unable to process traffic normally.
“I can just spin up a thousand builders, rotate them, offer very high bids, and not produce payloads,” Potuz said. “Any teenager can do this.”
The threat is limited to Sepolia, Ethereum’s test network, where test ether has no meaningful financial value. It does not put funds on Ethereum mainnet at risk. However, missing transaction payloads could interfere with the infrastructure testing needed to determine whether Glamsterdam is ready for a live launch.
Fake Builders Could Disrupt Block Production
Glamsterdam introduces changes to how Ethereum validators and specialized block builders work together. Builders assemble transaction blocks and compete through bids, while validators select a winning proposal. The builder is then expected to reveal the transaction payload behind that block.
On a free testnet, an attacker could exploit this process by submitting bids far above legitimate competitors, winning repeatedly and withholding the promised data.
Existing safeguards generally allow validators to fall back to locally built blocks after several payloads go missing. Developers said that may not be enough if attackers can repeatedly return under new identities.
Potuz argued that Ethereum clients should be able to identify and reject individual builders, preventing malicious operators from simply creating fresh accounts and continuing the attack.
Glamsterdam Targets Higher Network Capacity
The upgrade is designed to allow Ethereum to process more activity in each block without placing excessive demands on the computers that verify transactions.
Changes to gas pricing are expected to support a block gas limit of around 200 million, creating more room for payments and trades before network congestion pushes transaction fees higher.
A large private rehearsal completed the Glamsterdam transition one day before the developer call. The test also raised the block gas limit toward 200 million without losing finality, giving developers an early indication that the upgrade can handle the proposed changes.
Shorter Testing Window Raises Pressure
Client teams have until September 29 to release software ready for the Sepolia fork. That leaves just seven days before the October 6 test, compared with the 14-day period normally reserved for Ethereum upgrade security reviews and bug-bounty testing.
Developers accepted the shorter window because Sepolia is relatively centralized and can be recovered more easily if problems arise.
However, production builder software operated by Titan and Ultrasound has not yet completed the Glamsterdam transition. That leaves additional work before the upgrade can be considered ready for Ethereum mainnet.
The next public test on Hoodi is tentatively planned for October 27. Developers will decide whether to keep that date after reviewing the Sepolia results.
A mainnet activation date has not yet been scheduled.