Ethereum's Glamsterdam Upgrade Hits Sepolia Testnet

Ethereum is about to flip the switch on its biggest network upgrade in years, and the rehearsal happens on a chain nobody's money touches. The Glamsterdam upgrade activates on the Sepolia testnet this Tuesday, October 6, 2026, at roughly 13:53 UTC, giving developers their first public look at changes that could triple how much activity fits in each Ethereum block. If the testnet fork goes cleanly, a mainnet date for the fourth quarter of 2026 gets a lot more likely.

Glamsterdam is the next hard fork in Ethereum's roadmap, following this year's Fusaka upgrade. The name pairs the execution-layer half, Amsterdam, with the consensus-layer half, Gloas, following the network's Devconnect naming convention. The fork bundles ten proposals across both layers and aims at three goals: faster processing, more capacity, and less database bloat.

What the Glamsterdam upgrade actually changes

The headline change is enshrined proposer-builder separation, the proposal known as EIP-7732. Today, almost every Ethereum block is assembled by specialized outside firms called builders, and the traffic flows through off-chain relays with no protocol accountability. According to analysis of live network data, more than 90 percent of blocks are built through the MEV-Boost relay system, with the four largest builders responsible for the vast majority of them, a concentration score that would raise eyebrows in any other market. The Glamsterdam upgrade writes the builder role directly into the consensus rules: builders become staked actors in the protocol, a validator commits to the winning bid, and a new timeliness committee attests that the builder revealed the transaction data on schedule.

The second headline is block-level access lists, or BALs. By declaring which accounts and storage slots a block will touch, the network can prefetch data and validate transactions in parallel instead of one by one. That parallelization is the key that lets the Glamsterdam upgrade raise the block gas limit safely: a private rehearsal called Devnet-11 already ran 84,000 simulated validators at the new, tripled capacity without losing finality, which is what cleared the way for the Sepolia test.

Then there is the part users will feel most directly: gas repricing. Two proposals reprice how the network charges for state, the permanent records its computers must keep. Creating a new account or storage entry will cost more, and reading existing state gets repriced too. The most talked-about example, as reported by CoinDesk, is a new category called "state gas": under the Glamsterdam upgrade, sending ETH to an address that has never appeared on the network will carry a charge of 183,600 units of it on top of the familiar 21,000 base fee, breaking one of Ethereum's oldest rules of thumb. The Foundation has told wallet makers, fee calculators, and blockchain trackers to update any software that treats 21,000 as both the floor and the ceiling for a transfer, or payments could get rejected or quoted short.

Why developers are watching the Sepolia test so closely

Moving the Glamsterdam upgrade to a public testnet is the standard midway point in Ethereum's process: it sits between private devnet rehearsals and the real mainnet activation, and it is where the wider ecosystem finally gets to break things. Sepolia is one of Ethereum's longest-running public test networks, used by app developers, infrastructure providers, and node operators to check their software against the change in something close to real-world conditions. A clean Glamsterdam upgrade fork on Sepolia typically clears the way for the next testnet, Hoodi, and then a mainnet date. Problems found here push timelines back while client teams fix them.

And developers have already flagged one problem to watch. According to CoinDesk, consensus developer Potuz warned during a September core-developer call that the new builder mechanics could be abused on a free test network: because test ETH costs nothing, a malicious operator could spin up thousands of fake builder identities, outbid legitimate builders for block space, and then simply refuse to release the transaction payloads. On mainnet, the cost of block space makes that attack expensive to sustain; on Sepolia, it is essentially free, and existing safeguards only fall back to locally built blocks after several payloads go missing.

Client teams were asked to ship Sepolia-ready software by late September, leaving a review window of about seven days, roughly half the normal period, which was accepted because Sepolia's validator set is relatively centralized and easier to recover. Production builder software run by major teams has also not yet completed a Glamsterdam upgrade transition, adding one more gap before the fork can be treated as mainnet-ready.

The bigger race: Ethereum versus Solana in October

Glamsterdam is not the only protocol rewrite landing this month. According to a detailed comparison published by CoinPedia, Solana's own major upgrade, Alpenglow, is live on its testnet and targeting an October mainnet window. The two upgrades aim at completely different bottlenecks, which makes the side-by-side telling: Ethereum is scaling how much fits in a block, while Solana is speeding up how fast a block is finalized.

Under the Glamsterdam upgrade, Ethereum's block gas limit climbs from 60 million toward 200 million, more than tripling execution capacity, though the network's roughly thirteen-minute finality window stays untouched.

Under Alpenglow's first phase, Solana would take voting transactions off-chain entirely, freeing the capacity that consensus housekeeping currently eats, and collapse finality from about 12.8 seconds to a target of 100 to 150 milliseconds, a cut of roughly 99 percent. Solana's upgrade cleared its validator governance vote back in September 2025 with more than 98 percent approval. Neither upgrade fixes what the other targets: Ethereum still finalizes slowly, and Solana's raw execution engine is not what Alpenglow upgrades.

What this means for regular ETH holders

For anyone holding ether rather than running infrastructure, the Glamsterdam upgrade asks for almost nothing, and that is worth saying plainly because upgrade seasons attract scammers. The Ethereum Foundation's guidance is that no token action is required: balances and accounts do not change, and anyone asking you to "migrate" or "upgrade" your ETH for the fork is running a scam. Mainnet users do not need to touch anything, while node operators on Sepolia must update both their execution and consensus software before activation or risk following an obsolete fork.

The realistic upside is cheaper, roomier transactions. With block space roughly tripling under the Glamsterdam upgrade, ordinary transfers should get meaningfully less expensive; one independent estimate puts simple ETH transfers at around 71 percent cheaper after the fork. The one practical check that matters is keeping wallet software current, since wallets and fee estimators that still assume the old gas rules can misfire until they update. Capacity, though, is not demand: a wider highway does not guarantee more traffic. Whether cheaper block space pulls activity back from cheaper layer-two networks, where fees have drifted well below mainnet levels this year, is a question that gets answered only after the mainnet switch flips. For now, Tuesday's Sepolia fork is the test that decides whether that switch stays on schedule.

For more on Ethereum's market backdrop, see how ether derivatives positioning has been shifting, and follow the network beat on the crypto topic page.