Ethereum Set Date for Glamsterdam Testing, but Developers Warned of Attack on Sepolia

Olena Kocherhina
Choose us on Google

• Ethereum will run the public Glamsterdam test on October 6.
• The upgrade is expected to boost network throughput by raising the gas limit to around 200 million.
• However, developers have found an issue during testing.

Ethereum developers have confirmed a public test of the Glamsterdam upgrade on October 6, 2026, but warned about a vulnerability in the new block auction system on the Sepolia testnet. CoinDesk reported this, citing a core developers call.

An attacker could spin up a large number of fake builder identities, outbid legitimate participants, and then fail to deliver transactions after winning, which could complicate infrastructure testing ahead of Glamsterdam’s mainnet rollout.

Glamsterdam Is Expected to Boost Ethereum Throughput

Glamsterdam will be Ethereum’s next major upgrade after Fusaka, which was launched on mainnet on December 3, 2025. Before that, on May 7, 2025, Pectra was successfully activated on mainnet — the network’s biggest upgrade since The Merge.

Glamsterdam is designed to pack more activity into each block without overloading the computers that verify the network. Alongside changes to gas accounting, the upgrade is expected to pave the way for a block gas limit of around 200 million, increasing the number of payments and trades that can be processed in a single block.

As part of Glamsterdam, validator interaction with specialized block builders will become part of the Ethereum protocol. Builders assemble blocks and compete with one another, and once the highest bid is accepted, the validator expects to receive the corresponding set of transactions.

At the same time, this system can be attacked relatively cheaply on a testnet, since test Ethereum has no meaningful value. According to Ethereum consensus-layer developer Potuz:

“I can just spin up a thousand builders, rotate them, offer very high bids, and not produce payloads. Any teenager can do this.”

The developers noted that existing protection mechanisms typically switch to locally built blocks only after several instances of missing data. That is why clients also need to learn to block specific builders, so an attacker cannot continue the attack under a new identity.

Sepolia Got Only Seven Days for Verification

The warning came the day after a large-scale private Glamsterdam rehearsal, during which the block gas limit was raised toward 200 million without losing finality.

Now client teams have until September 29 to release Sepolia-compatible software. That leaves only seven days until the fork — half the standard 14 days allocated for security checks and bug-bounty testing.

Developers agreed to the shortened timeline because Sepolia is a relatively centralized network that is easier to recover if issues arise. At the same time, the block-building software from the Titan and Ultrasound teams has not yet completed the transition to Glamsterdam.

The next public test on the Hoodi network is tentatively scheduled for October 27. The final decision will depend on Sepolia’s results, while the activation date for Glamsterdam on the Ethereum mainnet has not yet been set.

As a reminder, a month ago Ethereum launched the Platåberget testnet to validate Glamsterdam ahead of its rollout on Sepolia and Hoodi.

Source: incrypted.com