Ethereum schedules Sepolia Glamsterdam for Oct. 6 and warns of abusive builder tactics

Ethereum confirmed the dates for its Glamsterdam testing on Sepolia, with the test scheduled for Oct. 6 ^{[1] [2]}.

Ethereum also warned that “fake” or abusive builder behavior could stall testing by exploiting free test ether to win block auctions and then withhold transaction payloads ^{[1] [2]}.

One report said the described attack would be aimed at disrupting Sepolia test traffic and upgrade evaluation, and that it would not directly affect user funds on Ethereum mainnet ^[3].

Additional reporting tied the security concern to the Sepolia testing process for Glamsterdam, describing the risk that an attacker could gain an advantage over block bidding by using Sepolia testnet ETH that is available for free ^[4].

Client teams were reported to have a Sept. 29 deadline to release Sepolia-ready software, and Glamsterdam was described as targeting a block gas limit near 200 million to allow more activity per block ^[3].