Ethereum developers have confirmed October 6 as the test date for the highly anticipated Glamsterdam upgrade on the Sepolia network. At the same time, developers have warned that malicious actors could exploit cheap test ether to create fake builder identities, repeatedly win block auctions and withhold transaction data. Such an attack would not threaten funds on Ethereum’s mainnet, but it could disrupt Sepolia and make it harder to test the upgrade properly.
The concern is linked to Enshrined Proposer-Builder Separation, or ePBS, one of the major changes planned for Glamsterdam. The design moves the relationship between validators and specialised block builders into Ethereum’s protocol.
Builders assemble transaction blocks and compete by submitting bids. Once a validator accepts the winning bid, the builder is expected to provide the underlying transaction payload. On a public testnet, however, an attacker could create numerous identities, offer unusually high bids and then refuse to provide the promised data.
Consensus developer Potuz warned during an Ethereum developer call that an attacker could create thousands of builders, rotate their identities and repeatedly disrupt the process. Because test ether has little or no economic value, carrying out such behaviour is much cheaper on a test network than on mainnet.
Developers said the scenario is an availability and testing concern rather than a method of stealing mainnet funds. If blocks repeatedly arrive without transaction payloads, developers could struggle to test how Glamsterdam behaves under realistic conditions.
Existing safeguards may not immediately solve the problem. Some client systems can fall back to locally built blocks after missing payloads, but developers discussed the need for stronger mechanisms to identify and restrict individual abusive builders.
Glamsterdam is designed to increase Ethereum’s Layer 1 capacity while changing how blocks are constructed and verified. The upgrade includes ePBS, Block-Level Access Lists and changes to gas pricing. The planned configuration is intended to support a block gas limit of around 200 million, although that figure remains a testing parameter rather than a confirmed mainnet commitment.
The development schedule is also relatively compressed. Client teams are expected to have Sepolia-ready software by September 29, leaving about a week before the October 6 test. Developers acknowledged that this is shorter than the normal 14-day period used for security reviews and bug-bounty testing.
The next public test on Hoodi is tentatively planned for October 27, although developers will assess Sepolia before deciding whether to keep that date. Ethereum’s mainnet activation date has not yet been scheduled.
Ethereum’s Glamsterdam upgrade heads to Sepolia on October 6.
Developers warn malicious builders could disrupt testing by withholding transaction data. No mainnet launch date is confirmed.
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For now, the October 6 Sepolia test is the next major checkpoint. Developers will use it to examine both Glamsterdam’s technical performance and whether the builder system can withstand the kind of adversarial behaviour that may not appear during controlled private testing.
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