Ethereum Sets October 6 Glamsterdam Test as Developers Flag Builder-Auction Risk

Glamsterdam activated on Ethereum’s Sepolia testnet on October 6, 2026, at 13:53:36 UTC, according to a proposal merged through Ethereum’s protocol-management process. The activation occurred at epoch 353024 and slot 11296768, marking the first major public test of the planned upgrade. Developers have warned that Sepolia’s freely available ETH and easily replaceable builder identities could let an attacker repeatedly disrupt Glamsterdam’s block-building auctions by withholding promised transaction payloads; the testing risk does not threaten funds on Ethereum mainnet.

Sepolia Glamsterdam activated on October 6

The October 6 activation moved Glamsterdam into public-testnet testing on Sepolia. Ethereum’s official Glamsterdam roadmap page still refers to devnet testing, but that wording has not caught up with the Sepolia milestone; the upgrade’s fourth-quarter 2026 mainnet target remains undated.

Glamsterdam is focused on scaling changes, including enshrined proposer-builder separation, or ePBS. The approach changes how Ethereum’s block proposal process handles the relationship between validators proposing blocks and builders assembling their execution payloads.

Sepolia is therefore more than a date-setting exercise. It is the environment in which developers can examine how the new design behaves under testnet conditions before any decision is made on moving further through the rollout path.

Free Sepolia ETH could let fake builders repeatedly win auctions

CoinDesk reported that free Sepolia ETH and disposable builder identities could allow an attacker to repeatedly win block-building auctions and then withhold promised transaction payloads.

The participant could return under a new identity after disrupting an auction, and the low-cost testnet ETH would remove the financial friction of repeated bids. The reported scenario concerns interference with testing rather than value extraction, and the risk remains limited to Sepolia: it does not threaten mainnet funds, although persistent withheld payloads could stall or complicate testing of Glamsterdam’s auction and delivery mechanics.

Enshrined proposer-builder separation makes payload delivery the test

Glamsterdam’s ePBS design, outlined in EIP-7732, has builders commit to execution payloads for later reveal rather than deliver them at the initial commitment. Payload-timeliness committees would monitor whether winning builders complete that delivery.

Sepolia will test the arrangement in conditions where free testnet ETH and disposable builder identities could support repeated auction wins followed by withheld payloads. The specific concern raised by developers is a winning builder that fails to reveal its payload, potentially disrupting Glamsterdam testing; the risk remains limited to testing and does not threaten mainnet funds.

Hoodi remains tentative as mainnet timing stays undecided

The September 17 All Core Developers consensus call recorded October 6 for Sepolia and tentatively discussed October 27 for Hoodi. The discussion did not set a mainnet fork date.

Sepolia’s October 6 activation is now the first completed public-testnet milestone. The deployment is testing ePBS, block-level access lists and gas-market changes, including a planned 200 million gas limit—more than three times Sepolia’s prior roughly 60 million limit.

The official roadmap targets Glamsterdam mainnet deployment in the fourth quarter of 2026, but the target does not establish a final launch timetable. Following Sepolia’s activation, Glamsterdam is in public-testnet testing rather than devnet-only testing.

Disclaimer: This article is provided for informational purposes only. It is not offered or intended to be used as legal, tax, investment, financial, or other advice.