Ethereum’s Glamsterdam Upgrade Slipped Again. Sepolia Now Targets October 6

Ethereum (CRYPTO:ETH) developers tentatively set October 6 at 13:53 UTC as the activation date for the Glamsterdam upgrade on the Sepolia testnet, an agreement reached at the ACDC #186 developer call on September 3. 

Glamsterdam’s Sepolia activation was first scheduled for August 3, and the upgrade’s overall mainnet target slipped from the first half of 2026 to the fourth quarter back in August. We examine what is holding up the timeline and whether October 6 still holds.

How Many Times Has Glamsterdam’s Timeline Slipped?

Ethereum developers originally targeted Glamsterdam for the first half of 2026. Developers pushed that target back to the fourth quarter of 2026 in mid-August, after Platåberget, Glamsterdam’s first dedicated public test network, went live. Platåberget’s launch confirmed the upgrade needed more testing time than developers had originally planned. 

Sepolia’s own date moved on a separate timeline. Developers first scheduled Glamsterdam’s Sepolia activation for August 3, then pushed it back as the devnet phase ran longer than expected. Nine devnets ran in sequence, numbered 0 through 9, between late March and early September, before developers agreed on the October 6 target at the September 3 ACDC meeting. That timeline puts Sepolia’s activation about two months behind its original schedule.

What’s Actually Blocking a Stable Devnet?

Four specific problems have kept Glamsterdam from running cleanly on a private devnet.

Devnet-9’s Finalization Problem

Devnet-9 launched on September 1 with 1,000 validator nodes and still cannot finalize blocks normally. Finality is the point at which a block becomes permanent and cannot be reversed, the same guarantee that makes a transaction safe to treat as settled. 

Ethereum’s mainnet has finalized blocks without interruption for years, which is part of why a devnet that cannot finalize consistently draws this much attention before any upgrade moves forward.

The Devnet-8 Consensus Bug

Devnet-8, the test network before Devnet-9, exposed a bug in Glamsterdam’s consensus layer, the part of the protocol that gets validators to agree on which blocks are valid, serious enough that it could have stopped the entire network from running. 

Consensus-layer bugs draw more scrutiny than most other issues because they threaten the basic agreement that keeps every node on the same chain, rather than affecting a single feature.

EIP-8037’s Execution-Layer Issue

EIP-8037 introduces a state gas dimension, an additional gas cost applied specifically to transactions that create new accounts on the network. Developers found an issue in how that change was implemented on the execution layer, the part of the protocol that processes transactions, which required every execution client team to revise their code before testing could continue. 

The Ethereum Foundation has already warned that tools treating gas limits as fixed values will stop working once Glamsterdam activates, which means wallets, indexers, and gas estimation tools all need updates before the upgrade reaches mainnet.

Devnet-11 Replacing Devnet-10

Developers skipped Devnet-10 and moved straight to Devnet-11, launching September 14 with 84,000 validators, 84 times the validator count Devnet-9 ran with. A larger validator set tests the upgrade under conditions closer to Ethereum’s mainnet, which runs far more validators than any devnet has tested so far, so a stable run on Devnet-11 would carry more weight than a stable run on a smaller test network. Devnet-11’s Gloas fork, the specific software update it will test, is scheduled two days later, on September 16.

Would October 6 Hold This Time?

No official All Core Developers meeting has locked in a mainnet block height, and developers have said correctness takes priority over hitting any specific date, so October 6 remains conditional.

Four steps stand between Glamsterdam and mainnet. First, Devnet-11 needs to run stably, with Sepolia’s October 6 activation depending on that stability holding. Hoodi, the second public testnet, comes next, even though developers haven’t set a date because they are waiting for Sepolia to go smoothly first. Mainnet activation follows Hoodi, with the fourth quarter of 2026 as the current roadmap target and December discussed informally as a possible window.

We think October 6 is more likely to slip again than to hold. Devnet-9 could not finalize as of early September, and developers have already replaced two planned steps, Devnet-10 and the original August 3 Sepolia date, once problems surfaced on the ones before them. September 14’s Devnet-11 launch is the next test to watch. If Devnet-11 finalizes cleanly and holds through its Gloas fork on September 16, October 6 becomes far more credible. If Devnet-11 repeats Devnet-9’s finalization problem, expect Sepolia to move again, and a December mainnet activation to become the more likely casualty.

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