Ethereum's Glamsterdam upgrade is set for the Sepolia testnet on October 6, giving developers their first live rehearsal of three changes bundled into one release: proposer-builder separation, block-level access lists, and a new gas pricing model. There's no mainnet date yet, and that's the detail worth watching.
Sepolia first, mainnet whenever
Sepolia is a public test network, which makes it the natural place to shake out code before anything touches real money. October 6 is the date. If the testnet run surfaces problems — and upgrade rehearsals often do — the mainnet timeline slips until they're fixed.
That's the normal rhythm for Ethereum upgrades, and it's why the absence of a mainnet date isn't a red flag. It's the process working as intended.
Proposer-builder separation, explained plainly
Proposer-builder separation, or PBS, splits a job that currently sits with one party. Today, a validator that proposes a block can also decide how that block gets assembled and ordered. PBS hands the building side to specialized actors and leaves the proposing side to validators.
The pitch is less centralization risk and better block construction. Whether that holds up in practice depends on the builder market that forms around it.
Access lists and the gas rethink
Block-level access lists are the second piece. They let a block declare upfront which accounts and storage slots it will touch, so clients can process transactions in parallel instead of one at a time.
The third change is new gas pricing. Gas is how Ethereum meters computational work, and the current schedule has been criticized for mispricing certain operations. Glamsterdam adjusts it.
Those three changes are the whole of what's been confirmed for this upgrade. No surprise add-ons, no last-minute scope creep that anyone has announced.
What to watch on October 6
Sepolia isn't carrying user funds, so the stakes are lower than mainnet. But testnet behavior is the signal developers use to decide whether the code is ready.
The concrete next thing is the October 6 activation itself. After that, the question is whether the mainnet date gets set — and nobody has said when that announcement will come.
